diff --git a/build-common/test/org/jetbrains/kotlin/metadata/DebugProtoBuf.java b/build-common/test/org/jetbrains/kotlin/metadata/DebugProtoBuf.java
index e3d0de92bd6..a2b354548fe 100644
--- a/build-common/test/org/jetbrains/kotlin/metadata/DebugProtoBuf.java
+++ b/build-common/test/org/jetbrains/kotlin/metadata/DebugProtoBuf.java
@@ -10100,6 +10100,7 @@ public final class DebugProtoBuf {
      *isExternal
      *isExpect
      *isInline
+     *isFun
      * </pre>
      */
     boolean hasFlags();
@@ -10116,6 +10117,7 @@ public final class DebugProtoBuf {
      *isExternal
      *isExpect
      *isInline
+     *isFun
      * </pre>
      */
     int getFlags();
@@ -10853,6 +10855,7 @@ public final class DebugProtoBuf {
      *isExternal
      *isExpect
      *isInline
+     *isFun
      * </pre>
      */
     public boolean hasFlags() {
@@ -10871,6 +10874,7 @@ public final class DebugProtoBuf {
      *isExternal
      *isExpect
      *isInline
+     *isFun
      * </pre>
      */
     public int getFlags() {
@@ -12242,6 +12246,7 @@ public final class DebugProtoBuf {
        *isExternal
        *isExpect
        *isInline
+       *isFun
        * </pre>
        */
       public boolean hasFlags() {
@@ -12260,6 +12265,7 @@ public final class DebugProtoBuf {
        *isExternal
        *isExpect
        *isInline
+       *isFun
        * </pre>
        */
       public int getFlags() {
@@ -12278,6 +12284,7 @@ public final class DebugProtoBuf {
        *isExternal
        *isExpect
        *isInline
+       *isFun
        * </pre>
        */
       public Builder setFlags(int value) {
@@ -12299,6 +12306,7 @@ public final class DebugProtoBuf {
        *isExternal
        *isExpect
        *isInline
+       *isFun
        * </pre>
        */
       public Builder clearFlags() {
diff --git a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrDeclarationStorage.kt b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrDeclarationStorage.kt
index 66349b64f71..99d07495113 100644
--- a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrDeclarationStorage.kt
+++ b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrDeclarationStorage.kt
@@ -168,7 +168,8 @@ class Fir2IrDeclarationStorage(
                         isData = regularClass?.isData == true,
                         isExternal = regularClass?.isExternal == true,
                         isInline = regularClass?.isInline == true,
-                        isExpect = regularClass?.isExpect == true
+                        isExpect = regularClass?.isExpect == true,
+                        isFun = false // TODO
                     ).apply {
                         descriptor.bind(this)
                         if (setParent && regularClass != null) {
@@ -215,7 +216,8 @@ class Fir2IrDeclarationStorage(
                     startOffset, endOffset, origin, symbol,
                     Name.special("<no name provided>"), anonymousObject.classKind,
                     Visibilities.LOCAL, modality,
-                    isCompanion = false, isInner = false, isData = false, isExternal = false, isInline = false, isExpect = false
+                    isCompanion = false, isInner = false, isData = false, isExternal = false,
+                    isInline = false, isExpect = false, isFun = false
                 ).apply {
                     descriptor.bind(this)
                     declareThisReceiver()
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/psi/synthetics/SyntheticClassOrObjectDescriptor.kt b/compiler/frontend/src/org/jetbrains/kotlin/psi/synthetics/SyntheticClassOrObjectDescriptor.kt
index 2b08cde5dfa..070ad1fa064 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/psi/synthetics/SyntheticClassOrObjectDescriptor.kt
+++ b/compiler/frontend/src/org/jetbrains/kotlin/psi/synthetics/SyntheticClassOrObjectDescriptor.kt
@@ -82,6 +82,7 @@ class SyntheticClassOrObjectDescriptor(
     override fun isInline() = false
     override fun isExpect() = false
     override fun isActual() = false
+    override fun isFun() = false
 
     override fun getCompanionObjectDescriptor(): ClassDescriptorWithResolutionScopes? = null
     override fun getTypeConstructor(): TypeConstructor = typeConstructor
diff --git a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/descriptors/LazyClassDescriptor.java b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/descriptors/LazyClassDescriptor.java
index 8d6baaeedf2..641af53c4a5 100644
--- a/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/descriptors/LazyClassDescriptor.java
+++ b/compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/descriptors/LazyClassDescriptor.java
@@ -86,6 +86,7 @@ public class LazyClassDescriptor extends ClassDescriptorBase implements ClassDes
     private final boolean isInline;
     private final boolean isExpect;
     private final boolean isActual;
+    private final boolean isFun;
 
     private final Annotations annotations;
     private final Annotations danglingAnnotations;
@@ -158,6 +159,8 @@ public class LazyClassDescriptor extends ClassDescriptorBase implements ClassDes
         this.isExpect = modifierList != null && PsiUtilsKt.hasExpectModifier(modifierList) ||
                         containingDeclaration instanceof ClassDescriptor && ((ClassDescriptor) containingDeclaration).isExpect();
 
+        this.isFun = modifierList != null && PsiUtilsKt.hasFunModifier(modifierList);
+
         // Annotation entries are taken from both own annotations (if any) and object literal annotations (if any)
         List<KtAnnotationEntry> annotationEntries = new ArrayList<>();
         if (classOrObject != null && classOrObject.getParent() instanceof KtObjectLiteralExpression) {
@@ -533,6 +536,11 @@ public class LazyClassDescriptor extends ClassDescriptorBase implements ClassDes
         return isActual;
     }
 
+    @Override
+    public boolean isFun() {
+        return isFun;
+    }
+
     @NotNull
     @Override
     public Annotations getAnnotations() {
diff --git a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/AbstractSuspendFunctionsLowering.kt b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/AbstractSuspendFunctionsLowering.kt
index a9339f691bd..5521bcb25f0 100644
--- a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/AbstractSuspendFunctionsLowering.kt
+++ b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/AbstractSuspendFunctionsLowering.kt
@@ -294,7 +294,8 @@ abstract class AbstractSuspendFunctionsLowering<C : CommonBackendContext>(val co
                 isData = false,
                 isExternal = false,
                 isInline = false,
-                isExpect = false
+                isExpect = false,
+                isFun = false
             ).apply {
                 d.bind(this)
                 parent = irFunction.parent
diff --git a/compiler/ir/backend.common/src/org/jetbrains/kotlin/ir/builders/declarations/declarationBuilders.kt b/compiler/ir/backend.common/src/org/jetbrains/kotlin/ir/builders/declarations/declarationBuilders.kt
index 511b8f5348d..a5ce2ff1746 100644
--- a/compiler/ir/backend.common/src/org/jetbrains/kotlin/ir/builders/declarations/declarationBuilders.kt
+++ b/compiler/ir/backend.common/src/org/jetbrains/kotlin/ir/builders/declarations/declarationBuilders.kt
@@ -26,7 +26,8 @@ fun IrClassBuilder.buildClass(): IrClass {
         startOffset, endOffset, origin,
         IrClassSymbolImpl(wrappedDescriptor),
         name, kind, visibility, modality,
-        isCompanion = isCompanion, isInner = isInner, isData = isData, isExternal = isExternal, isInline = isInline, isExpect = isExpect
+        isCompanion = isCompanion, isInner = isInner, isData = isData, isExternal = isExternal,
+        isInline = isInline, isExpect = isExpect, isFun = isFun
     ).also {
         wrappedDescriptor.bind(it)
     }
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsSharedVariablesManager.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsSharedVariablesManager.kt
index e5fb16c9398..e051a448181 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsSharedVariablesManager.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsSharedVariablesManager.kt
@@ -126,7 +126,8 @@ class JsSharedVariablesManager(val builtIns: IrBuiltIns, val implicitDeclaration
         val declaration = IrClassImpl(
             UNDEFINED_OFFSET, UNDEFINED_OFFSET, JsLoweredDeclarationOrigin.JS_CLOSURE_BOX_CLASS_DECLARATION, IrClassSymbolImpl(descriptor),
             Name.identifier(boxTypeName), ClassKind.CLASS, Visibilities.PUBLIC, Modality.FINAL,
-            isCompanion = false, isInner = false, isData = false, isExternal = false, isInline = false, isExpect = false
+            isCompanion = false, isInner = false, isData = false, isExternal = false,
+            isInline = false, isExpect = false, isFun = false
         )
 
         descriptor.bind(declaration)
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/descriptors/JvmDeclarationFactory.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/descriptors/JvmDeclarationFactory.kt
index 6e5b5c29406..484dbdce7e0 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/descriptors/JvmDeclarationFactory.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/descriptors/JvmDeclarationFactory.kt
@@ -236,7 +236,8 @@ class JvmDeclarationFactory(
                 isData = false,
                 isExternal = false,
                 isInline = false,
-                isExpect = false
+                isExpect = false,
+                isFun = false
             ).apply {
                 descriptor.bind(this)
                 parent = interfaceClass
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/FileClassLowering.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/FileClassLowering.kt
index d725431e104..5654a32a28c 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/FileClassLowering.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/FileClassLowering.kt
@@ -88,7 +88,8 @@ private class FileClassLowering(val context: JvmBackendContext) : FileLoweringPa
             isData = false,
             isExternal = false,
             isInline = false,
-            isExpect = false
+            isExpect = false,
+            isFun = false
         ).apply {
             descriptor.bind(this)
             superTypes.add(context.irBuiltIns.anyType)
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/builders/declarations/IrClassBuilder.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/builders/declarations/IrClassBuilder.kt
index 257dd31fa3a..c5b1f03788a 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/builders/declarations/IrClassBuilder.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/builders/declarations/IrClassBuilder.kt
@@ -19,6 +19,7 @@ class IrClassBuilder : IrDeclarationBuilder() {
     var isExternal: Boolean = false
     var isInline: Boolean = false
     var isExpect: Boolean = false
+    var isFun: Boolean = false
 
     fun updateFrom(from: IrClass) {
         super.updateFrom(from)
@@ -31,5 +32,6 @@ class IrClassBuilder : IrDeclarationBuilder() {
         isExternal = from.isExternal
         isInline = from.isInline
         isExpect = from.isExpect
+        isFun = from.isFun
     }
 }
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrClass.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrClass.kt
index d0d9eacdcea..65a20c8fd3e 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrClass.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrClass.kt
@@ -39,6 +39,7 @@ interface IrClass :
     val isExternal: Boolean
     val isInline: Boolean
     val isExpect: Boolean
+    val isFun: Boolean
 
     val superTypes: MutableList<IrType>
 
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrClassImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrClassImpl.kt
index e17bfd8ea8d..cd6eb0de4bd 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrClassImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrClassImpl.kt
@@ -44,7 +44,8 @@ class IrClassImpl(
     override val isData: Boolean,
     override val isExternal: Boolean,
     override val isInline: Boolean,
-    override val isExpect: Boolean
+    override val isExpect: Boolean,
+    override val isFun: Boolean
 ) :
     IrDeclarationBase(startOffset, endOffset, origin),
     IrClass {
@@ -66,7 +67,8 @@ class IrClassImpl(
                 isData = symbol.descriptor.isData,
                 isExternal = symbol.descriptor.isEffectivelyExternal(),
                 isInline = symbol.descriptor.isInline,
-                isExpect = symbol.descriptor.isExpect
+                isExpect = symbol.descriptor.isExpect,
+                isFun = symbol.descriptor.isFun
             )
 
     init {
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyClass.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyClass.kt
index c4dac814a3d..1222fc0d2b3 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyClass.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyClass.kt
@@ -35,6 +35,7 @@ class IrLazyClass(
     override val isExternal: Boolean,
     override val isInline: Boolean,
     override val isExpect: Boolean,
+    override val isFun: Boolean,
     stubGenerator: DeclarationStubGenerator,
     typeTranslator: TypeTranslator
 ) :
@@ -59,6 +60,7 @@ class IrLazyClass(
                 isExternal = symbol.descriptor.isEffectivelyExternal(),
                 isInline = symbol.descriptor.isInline,
                 isExpect = symbol.descriptor.isExpect,
+                isFun = symbol.descriptor.isFun,
                 stubGenerator = stubGenerator,
                 typeTranslator = TypeTranslator
             )
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/descriptors/WrappedDescriptors.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/descriptors/WrappedDescriptors.kt
index d585ee394ba..cf9a5a21cf9 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/descriptors/WrappedDescriptors.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/descriptors/WrappedDescriptors.kt
@@ -595,6 +595,8 @@ open class WrappedClassDescriptor(
 
     override fun isInline() = owner.isInline
 
+    override fun isFun() = owner.isFun
+
     override fun getThisAsReceiverParameter() = owner.thisReceiver?.descriptor as ReceiverParameterDescriptor
 
     override fun getUnsubstitutedPrimaryConstructor() =
@@ -705,6 +707,8 @@ open class WrappedEnumEntryDescriptor(
 
     override fun isInline() = false
 
+    override fun isFun() = false
+
     override fun getThisAsReceiverParameter() = (owner.parent as IrClass).descriptor.thisAsReceiverParameter
 
     override fun getUnsubstitutedPrimaryConstructor(): ClassConstructorDescriptor? {
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/DeepCopyIrTreeWithSymbols.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/DeepCopyIrTreeWithSymbols.kt
index 1430cdbe878..8cfa58ca911 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/DeepCopyIrTreeWithSymbols.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/DeepCopyIrTreeWithSymbols.kt
@@ -147,7 +147,8 @@ open class DeepCopyIrTreeWithSymbols(
             declaration.isData,
             declaration.isExternal,
             declaration.isInline,
-            declaration.isExpect
+            declaration.isExpect,
+            declaration.isFun
         ).apply {
             transformAnnotations(declaration)
             copyTypeParametersFrom(declaration)
diff --git a/compiler/ir/serialization.common/src/KotlinIr.proto b/compiler/ir/serialization.common/src/KotlinIr.proto
index 8d8aa973990..6afeab3fbaa 100644
--- a/compiler/ir/serialization.common/src/KotlinIr.proto
+++ b/compiler/ir/serialization.common/src/KotlinIr.proto
@@ -648,6 +648,7 @@ message IrClass {
   required IrDeclarationContainer declaration_container = 13;
   repeated int32 super_type = 14;
   required bool is_expect = 15;
+  required bool is_fun = 16;
 }
 
 message IrTypeAlias {
diff --git a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrFileDeserializer.kt b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrFileDeserializer.kt
index 3810546e4a7..5ed26eb9863 100644
--- a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrFileDeserializer.kt
+++ b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrFileDeserializer.kt
@@ -980,7 +980,8 @@ abstract class IrFileDeserializer(
                     isData = proto.isData,
                     isExternal = proto.isExternal,
                     isInline = proto.isInline,
-                    isExpect = proto.isExpect
+                    isExpect = proto.isExpect,
+                    isFun = proto.isFun
                 )
             }.usingParent {
                 proto.declarationContainer.declarationList.mapTo(declarations) { deserializeDeclaration(it) }
diff --git a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/proto/IrClass.java b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/proto/IrClass.java
index 77be52d4303..9c614d2a7a0 100644
--- a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/proto/IrClass.java
+++ b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/proto/IrClass.java
@@ -198,6 +198,11 @@ public final class IrClass extends
             isExpect_ = input.readBool();
             break;
           }
+          case 128: {
+            bitField0_ |= 0x00004000;
+            isFun_ = input.readBool();
+            break;
+          }
         }
       }
     } catch (org.jetbrains.kotlin.protobuf.InvalidProtocolBufferException e) {
@@ -475,6 +480,21 @@ public final class IrClass extends
     return isExpect_;
   }
 
+  public static final int IS_FUN_FIELD_NUMBER = 16;
+  private boolean isFun_;
+  /**
+   * <code>required bool is_fun = 16;</code>
+   */
+  public boolean hasIsFun() {
+    return ((bitField0_ & 0x00004000) == 0x00004000);
+  }
+  /**
+   * <code>required bool is_fun = 16;</code>
+   */
+  public boolean getIsFun() {
+    return isFun_;
+  }
+
   private void initFields() {
     base_ = org.jetbrains.kotlin.backend.common.serialization.proto.IrDeclarationBase.getDefaultInstance();
     name_ = 0;
@@ -491,6 +511,7 @@ public final class IrClass extends
     declarationContainer_ = org.jetbrains.kotlin.backend.common.serialization.proto.IrDeclarationContainer.getDefaultInstance();
     superType_ = java.util.Collections.emptyList();
     isExpect_ = false;
+    isFun_ = false;
   }
   private byte memoizedIsInitialized = -1;
   public final boolean isInitialized() {
@@ -550,6 +571,10 @@ public final class IrClass extends
       memoizedIsInitialized = 0;
       return false;
     }
+    if (!hasIsFun()) {
+      memoizedIsInitialized = 0;
+      return false;
+    }
     if (!getBase().isInitialized()) {
       memoizedIsInitialized = 0;
       return false;
@@ -624,6 +649,9 @@ public final class IrClass extends
     if (((bitField0_ & 0x00002000) == 0x00002000)) {
       output.writeBool(15, isExpect_);
     }
+    if (((bitField0_ & 0x00004000) == 0x00004000)) {
+      output.writeBool(16, isFun_);
+    }
     output.writeRawBytes(unknownFields);
   }
 
@@ -698,6 +726,10 @@ public final class IrClass extends
       size += org.jetbrains.kotlin.protobuf.CodedOutputStream
         .computeBoolSize(15, isExpect_);
     }
+    if (((bitField0_ & 0x00004000) == 0x00004000)) {
+      size += org.jetbrains.kotlin.protobuf.CodedOutputStream
+        .computeBoolSize(16, isFun_);
+    }
     size += unknownFields.size();
     memoizedSerializedSize = size;
     return size;
@@ -822,6 +854,8 @@ public final class IrClass extends
       bitField0_ = (bitField0_ & ~0x00002000);
       isExpect_ = false;
       bitField0_ = (bitField0_ & ~0x00004000);
+      isFun_ = false;
+      bitField0_ = (bitField0_ & ~0x00008000);
       return this;
     }
 
@@ -906,6 +940,10 @@ public final class IrClass extends
         to_bitField0_ |= 0x00002000;
       }
       result.isExpect_ = isExpect_;
+      if (((from_bitField0_ & 0x00008000) == 0x00008000)) {
+        to_bitField0_ |= 0x00004000;
+      }
+      result.isFun_ = isFun_;
       result.bitField0_ = to_bitField0_;
       return result;
     }
@@ -964,6 +1002,9 @@ public final class IrClass extends
       if (other.hasIsExpect()) {
         setIsExpect(other.getIsExpect());
       }
+      if (other.hasIsFun()) {
+        setIsFun(other.getIsFun());
+      }
       setUnknownFields(
           getUnknownFields().concat(other.unknownFields));
       return this;
@@ -1022,6 +1063,10 @@ public final class IrClass extends
         
         return false;
       }
+      if (!hasIsFun()) {
+        
+        return false;
+      }
       if (!getBase().isInitialized()) {
         
         return false;
@@ -1742,6 +1787,38 @@ public final class IrClass extends
       return this;
     }
 
+    private boolean isFun_ ;
+    /**
+     * <code>required bool is_fun = 16;</code>
+     */
+    public boolean hasIsFun() {
+      return ((bitField0_ & 0x00008000) == 0x00008000);
+    }
+    /**
+     * <code>required bool is_fun = 16;</code>
+     */
+    public boolean getIsFun() {
+      return isFun_;
+    }
+    /**
+     * <code>required bool is_fun = 16;</code>
+     */
+    public Builder setIsFun(boolean value) {
+      bitField0_ |= 0x00008000;
+      isFun_ = value;
+      
+      return this;
+    }
+    /**
+     * <code>required bool is_fun = 16;</code>
+     */
+    public Builder clearIsFun() {
+      bitField0_ = (bitField0_ & ~0x00008000);
+      isFun_ = false;
+      
+      return this;
+    }
+
     // @@protoc_insertion_point(builder_scope:org.jetbrains.kotlin.backend.common.serialization.proto.IrClass)
   }
 
diff --git a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/proto/IrClassOrBuilder.java b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/proto/IrClassOrBuilder.java
index 3b8911e6f27..8eb261aaaa0 100644
--- a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/proto/IrClassOrBuilder.java
+++ b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/proto/IrClassOrBuilder.java
@@ -153,4 +153,13 @@ public interface IrClassOrBuilder extends
    * <code>required bool is_expect = 15;</code>
    */
   boolean getIsExpect();
+
+  /**
+   * <code>required bool is_fun = 16;</code>
+   */
+  boolean hasIsFun();
+  /**
+   * <code>required bool is_fun = 16;</code>
+   */
+  boolean getIsFun();
 }
\ No newline at end of file
diff --git a/compiler/psi/src/org/jetbrains/kotlin/psi/psiUtil/psiUtils.kt b/compiler/psi/src/org/jetbrains/kotlin/psi/psiUtil/psiUtils.kt
index 03308f75970..2f90b4bfb3a 100644
--- a/compiler/psi/src/org/jetbrains/kotlin/psi/psiUtil/psiUtils.kt
+++ b/compiler/psi/src/org/jetbrains/kotlin/psi/psiUtil/psiUtils.kt
@@ -445,6 +445,8 @@ fun KtModifierListOwner.hasActualModifier() = hasModifier(KtTokens.IMPL_KEYWORD)
 fun KtModifierList.hasActualModifier() = hasModifier(KtTokens.IMPL_KEYWORD) || hasModifier(KtTokens.ACTUAL_KEYWORD)
 fun KtModifierList.hasSuspendModifier() = hasModifier(KtTokens.SUSPEND_KEYWORD)
 
+fun KtModifierList.hasFunModifier() = hasModifier(KtTokens.FUN_KEYWORD)
+
 fun ASTNode.children() = generateSequence(firstChildNode) { node -> node.treeNext }
 fun ASTNode.parents() = generateSequence(treeParent) { node -> node.treeParent }
 
diff --git a/compiler/serialization/src/org/jetbrains/kotlin/serialization/DescriptorSerializer.kt b/compiler/serialization/src/org/jetbrains/kotlin/serialization/DescriptorSerializer.kt
index 076a658c155..31a7857c210 100644
--- a/compiler/serialization/src/org/jetbrains/kotlin/serialization/DescriptorSerializer.kt
+++ b/compiler/serialization/src/org/jetbrains/kotlin/serialization/DescriptorSerializer.kt
@@ -69,7 +69,8 @@ class DescriptorSerializer private constructor(
             ProtoEnumFlags.visibility(normalizeVisibility(classDescriptor)),
             ProtoEnumFlags.modality(classDescriptor.modality),
             ProtoEnumFlags.classKind(classDescriptor.kind, classDescriptor.isCompanionObject),
-            classDescriptor.isInner, classDescriptor.isData, classDescriptor.isExternal, classDescriptor.isExpect, classDescriptor.isInline
+            classDescriptor.isInner, classDescriptor.isData, classDescriptor.isExternal, classDescriptor.isExpect,
+            classDescriptor.isInline, classDescriptor.isFun
         )
         if (flags != builder.flags) {
             builder.flags = flags
diff --git a/core/descriptors.jvm/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaClassDescriptor.kt b/core/descriptors.jvm/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaClassDescriptor.kt
index 654ef1a9a07..57009e6c3d7 100644
--- a/core/descriptors.jvm/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaClassDescriptor.kt
+++ b/core/descriptors.jvm/src/org/jetbrains/kotlin/load/java/lazy/descriptors/LazyJavaClassDescriptor.kt
@@ -97,6 +97,7 @@ class LazyJavaClassDescriptor(
     override fun isCompanionObject() = false
     override fun isExpect() = false
     override fun isActual() = false
+    override fun isFun() = false
 
     private val typeConstructor = LazyJavaClassTypeConstructor()
     override fun getTypeConstructor(): TypeConstructor = typeConstructor
diff --git a/core/descriptors/src/org/jetbrains/kotlin/builtins/functions/FunctionClassDescriptor.kt b/core/descriptors/src/org/jetbrains/kotlin/builtins/functions/FunctionClassDescriptor.kt
index 1a228159e9b..3ab74eca96d 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/builtins/functions/FunctionClassDescriptor.kt
+++ b/core/descriptors/src/org/jetbrains/kotlin/builtins/functions/FunctionClassDescriptor.kt
@@ -95,6 +95,7 @@ class FunctionClassDescriptor(
     override fun isInner() = false
     override fun isData() = false
     override fun isInline() = false
+    override fun isFun() = false
     override fun isExpect() = false
     override fun isActual() = false
     override fun isExternal() = false
diff --git a/core/descriptors/src/org/jetbrains/kotlin/descriptors/ClassDescriptor.java b/core/descriptors/src/org/jetbrains/kotlin/descriptors/ClassDescriptor.java
index 36e7f298c70..02133a552df 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/descriptors/ClassDescriptor.java
+++ b/core/descriptors/src/org/jetbrains/kotlin/descriptors/ClassDescriptor.java
@@ -70,6 +70,8 @@ public interface ClassDescriptor extends ClassifierDescriptorWithTypeParameters,
 
     boolean isInline();
 
+    boolean isFun();
+
     @NotNull
     ReceiverParameterDescriptor getThisAsReceiverParameter();
 
diff --git a/core/descriptors/src/org/jetbrains/kotlin/descriptors/NotFoundClasses.kt b/core/descriptors/src/org/jetbrains/kotlin/descriptors/NotFoundClasses.kt
index 0cc097f4d1e..c9591988ece 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/descriptors/NotFoundClasses.kt
+++ b/core/descriptors/src/org/jetbrains/kotlin/descriptors/NotFoundClasses.kt
@@ -69,6 +69,7 @@ class NotFoundClasses(private val storageManager: StorageManager, private val mo
         override fun isCompanionObject() = false
         override fun isData() = false
         override fun isInline() = false
+        override fun isFun() = false
         override fun isExpect() = false
         override fun isActual() = false
         override fun isExternal() = false
diff --git a/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/ClassDescriptorImpl.java b/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/ClassDescriptorImpl.java
index a0cc195df4a..e9a3ada4b1b 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/ClassDescriptorImpl.java
+++ b/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/ClassDescriptorImpl.java
@@ -144,6 +144,11 @@ public class ClassDescriptorImpl extends ClassDescriptorBase {
         return false;
     }
 
+    @Override
+    public boolean isFun() {
+        return false;
+    }
+
     @Override
     public boolean isInner() {
         return false;
diff --git a/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/EnumEntrySyntheticClassDescriptor.java b/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/EnumEntrySyntheticClassDescriptor.java
index 4eda4b8ce17..ad5f701ba28 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/EnumEntrySyntheticClassDescriptor.java
+++ b/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/EnumEntrySyntheticClassDescriptor.java
@@ -138,6 +138,11 @@ public class EnumEntrySyntheticClassDescriptor extends ClassDescriptorBase {
         return false;
     }
 
+    @Override
+    public boolean isFun() {
+        return false;
+    }
+
     @Override
     public boolean isCompanionObject() {
         return false;
diff --git a/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/LazySubstitutingClassDescriptor.java b/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/LazySubstitutingClassDescriptor.java
index 9de9cc8dec7..827371c5b5f 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/LazySubstitutingClassDescriptor.java
+++ b/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/LazySubstitutingClassDescriptor.java
@@ -243,6 +243,11 @@ public class LazySubstitutingClassDescriptor extends ModuleAwareClassDescriptor
         return original.isInline();
     }
 
+    @Override
+    public boolean isFun() {
+        return original.isFun();
+    }
+
     @Override
     public boolean isExternal() {
         return original.isExternal();
diff --git a/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/MutableClassDescriptor.java b/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/MutableClassDescriptor.java
index 5884475ee1b..831477747cd 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/MutableClassDescriptor.java
+++ b/core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/MutableClassDescriptor.java
@@ -99,6 +99,11 @@ public class MutableClassDescriptor extends ClassDescriptorBase {
         return false;
     }
 
+    @Override
+    public boolean isFun() {
+        return false;
+    }
+
     @Override
     public boolean isCompanionObject() {
         return false;
diff --git a/core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/descriptors/DeserializedClassDescriptor.kt b/core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/descriptors/DeserializedClassDescriptor.kt
index 349744290b2..521911899c4 100644
--- a/core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/descriptors/DeserializedClassDescriptor.kt
+++ b/core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/descriptors/DeserializedClassDescriptor.kt
@@ -104,6 +104,8 @@ class DeserializedClassDescriptor(
 
     override fun isExternal() = Flags.IS_EXTERNAL_CLASS.get(classProto.flags)
 
+    override fun isFun() = Flags.IS_FUN_INTERFACE.get(classProto.flags)
+
     override fun getUnsubstitutedMemberScope(kotlinTypeRefiner: KotlinTypeRefiner): MemberScope =
         memberScopeHolder.getScope(kotlinTypeRefiner)
 
diff --git a/core/metadata/src/metadata.proto b/core/metadata/src/metadata.proto
index 543298918c3..38e6418c3e0 100644
--- a/core/metadata/src/metadata.proto
+++ b/core/metadata/src/metadata.proto
@@ -209,6 +209,7 @@ message Class {
     isExternal
     isExpect
     isInline
+    isFun
   */
   optional int32 flags = 1 [default = 6 /* public final class, no annotations */];
 
diff --git a/core/metadata/src/org/jetbrains/kotlin/metadata/ProtoBuf.java b/core/metadata/src/org/jetbrains/kotlin/metadata/ProtoBuf.java
index f9e5fa99b2f..3847b3915e2 100644
--- a/core/metadata/src/org/jetbrains/kotlin/metadata/ProtoBuf.java
+++ b/core/metadata/src/org/jetbrains/kotlin/metadata/ProtoBuf.java
@@ -8273,6 +8273,7 @@ public final class ProtoBuf {
      *isExternal
      *isExpect
      *isInline
+     *isFun
      * </pre>
      */
     boolean hasFlags();
@@ -8289,6 +8290,7 @@ public final class ProtoBuf {
      *isExternal
      *isExpect
      *isInline
+     *isFun
      * </pre>
      */
     int getFlags();
@@ -8914,6 +8916,7 @@ public final class ProtoBuf {
      *isExternal
      *isExpect
      *isInline
+     *isFun
      * </pre>
      */
     public boolean hasFlags() {
@@ -8932,6 +8935,7 @@ public final class ProtoBuf {
      *isExternal
      *isExpect
      *isInline
+     *isFun
      * </pre>
      */
     public int getFlags() {
@@ -10059,6 +10063,7 @@ public final class ProtoBuf {
        *isExternal
        *isExpect
        *isInline
+       *isFun
        * </pre>
        */
       public boolean hasFlags() {
@@ -10077,6 +10082,7 @@ public final class ProtoBuf {
        *isExternal
        *isExpect
        *isInline
+       *isFun
        * </pre>
        */
       public int getFlags() {
@@ -10095,6 +10101,7 @@ public final class ProtoBuf {
        *isExternal
        *isExpect
        *isInline
+       *isFun
        * </pre>
        */
       public Builder setFlags(int value) {
@@ -10116,6 +10123,7 @@ public final class ProtoBuf {
        *isExternal
        *isExpect
        *isInline
+       *isFun
        * </pre>
        */
       public Builder clearFlags() {
diff --git a/core/metadata/src/org/jetbrains/kotlin/metadata/deserialization/Flags.java b/core/metadata/src/org/jetbrains/kotlin/metadata/deserialization/Flags.java
index 40dbbe58902..ab9c16dc328 100644
--- a/core/metadata/src/org/jetbrains/kotlin/metadata/deserialization/Flags.java
+++ b/core/metadata/src/org/jetbrains/kotlin/metadata/deserialization/Flags.java
@@ -30,6 +30,7 @@ public class Flags {
     public static final BooleanFlagField IS_EXTERNAL_CLASS = FlagField.booleanAfter(IS_DATA);
     public static final BooleanFlagField IS_EXPECT_CLASS = FlagField.booleanAfter(IS_EXTERNAL_CLASS);
     public static final BooleanFlagField IS_INLINE_CLASS = FlagField.booleanAfter(IS_EXPECT_CLASS);
+    public static final BooleanFlagField IS_FUN_INTERFACE = FlagField.booleanAfter(IS_INLINE_CLASS);
 
     // Constructors
 
@@ -95,7 +96,8 @@ public class Flags {
             boolean isData,
             boolean isExternal,
             boolean isExpect,
-            boolean isInline
+            boolean isInline,
+            boolean isFun
     ) {
         return HAS_ANNOTATIONS.toFlags(hasAnnotations)
                | MODALITY.toFlags(modality)
@@ -106,6 +108,7 @@ public class Flags {
                | IS_EXTERNAL_CLASS.toFlags(isExternal)
                | IS_EXPECT_CLASS.toFlags(isExpect)
                | IS_INLINE_CLASS.toFlags(isInline)
+               | IS_FUN_INTERFACE.toFlags(isFun)
                 ;
     }
 
diff --git a/konan/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/builder/CommonizedClassDescriptor.kt b/konan/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/builder/CommonizedClassDescriptor.kt
index c602e3d8ded..8728d82a64b 100644
--- a/konan/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/builder/CommonizedClassDescriptor.kt
+++ b/konan/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/builder/CommonizedClassDescriptor.kt
@@ -78,6 +78,7 @@ class CommonizedClassDescriptor(
     override fun isInner() = isInner
     override fun isExpect() = isExpect
     override fun isActual() = isActual
+    override fun isFun() = false // TODO: modifier "fun" should be accessible from here too
 
     override fun getUnsubstitutedMemberScope(kotlinTypeRefiner: KotlinTypeRefiner): CommonizedMemberScope {
         check(kotlinTypeRefiner == KotlinTypeRefiner.Default) {