diff --git a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/symbols/Fir2IrBindableSymbol.kt b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/symbols/Fir2IrBindableSymbol.kt
index b6bbf3969ae..375fc95c964 100644
--- a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/symbols/Fir2IrBindableSymbol.kt
+++ b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/symbols/Fir2IrBindableSymbol.kt
@@ -32,8 +32,6 @@ abstract class Fir2IrBindableSymbol<out D : DeclarationDescriptor, B : IrSymbolO
         }
     }
 
-    override val isPublicApi: Boolean = true
-
     override val isBound: Boolean
         get() = _owner != null
 
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/MoveBodilessDeclarationsToSeparatePlace.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/MoveBodilessDeclarationsToSeparatePlace.kt
index 13b3b76c899..371f0c2c74c 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/MoveBodilessDeclarationsToSeparatePlace.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/MoveBodilessDeclarationsToSeparatePlace.kt
@@ -59,11 +59,8 @@ private class DescriptorlessIrFileSymbol : IrFileSymbol {
 
     override val isBound get() = _owner != null
 
-    override val isPublicApi: Boolean
-        get() = error("Operation is unsupported")
-
-    override val signature: IdSignature
-        get() = error("Operation is unsupported")
+    override val signature: IdSignature?
+        get() = null
 }
 
 private fun isBuiltInClass(declaration: IrDeclaration): Boolean =
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/IrClassifierEqualityChecker.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/IrClassifierEqualityChecker.kt
index 11ad61fa45f..64c70d7348d 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/IrClassifierEqualityChecker.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/IrClassifierEqualityChecker.kt
@@ -14,8 +14,8 @@ interface IrClassifierEqualityChecker {
 object FqNameEqualityChecker : IrClassifierEqualityChecker {
     override fun areEqual(left: IrClassifierSymbol, right: IrClassifierSymbol): Boolean =
         left === right ||
-                left.isPublicApi && right.isPublicApi && left.signature == right.signature
+                left.signature != null && left.signature == right.signature
 
     override fun getHashCode(symbol: IrClassifierSymbol): Int =
-        if (symbol.isPublicApi) symbol.signature.hashCode() else symbol.hashCode()
+        symbol.signature?.hashCode() ?: symbol.hashCode()
 }
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/IrDelegatingSymbol.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/IrDelegatingSymbol.kt
index c1910aee720..a1cb38d2734 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/IrDelegatingSymbol.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/IrDelegatingSymbol.kt
@@ -18,10 +18,8 @@ abstract class IrDelegatingSymbol<S : IrBindableSymbol<D, B>, B : IrSymbolOwner,
     override val descriptor: D get() = delegate.descriptor
 
     override val isBound: Boolean get() = delegate.isBound
-    override val isPublicApi: Boolean
-        get() = delegate.isPublicApi
 
-    override val signature: IdSignature
+    override val signature: IdSignature?
         get() = delegate.signature
 
     override fun bind(owner: B) = delegate.bind(owner)
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/IrSymbol.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/IrSymbol.kt
index e8c814cec5f..ab78f3ece97 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/IrSymbol.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/IrSymbol.kt
@@ -32,9 +32,10 @@ interface IrSymbol {
 
     val isBound: Boolean
 
-    val signature: IdSignature
+    val signature: IdSignature?
 
     val isPublicApi: Boolean
+        get() = signature != null
 }
 
 interface IrBindableSymbol<out D : DeclarationDescriptor, B : IrSymbolOwner> : IrSymbol {
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/impl/DescriptorlessExternalPackageFragmentSymbol.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/impl/DescriptorlessExternalPackageFragmentSymbol.kt
index f436a6e7202..4cdd6225e3c 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/impl/DescriptorlessExternalPackageFragmentSymbol.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/impl/DescriptorlessExternalPackageFragmentSymbol.kt
@@ -22,7 +22,7 @@ class DescriptorlessExternalPackageFragmentSymbol : IrExternalPackageFragmentSym
     override val isPublicApi: Boolean
         get() = TODO("Not yet implemented")
 
-    override val signature: IdSignature
+    override val signature: IdSignature?
         get() = TODO("Not yet implemented")
 
     override val isBound get() = _owner != null
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/impl/IrPrivateSymbolBase.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/impl/IrPrivateSymbolBase.kt
index 75cae5a451d..1edb264ed7e 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/impl/IrPrivateSymbolBase.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/impl/IrPrivateSymbolBase.kt
@@ -69,10 +69,8 @@ abstract class IrBindableSymbolBase<out D : DeclarationDescriptor, B : IrSymbolO
         }
     }
 
-    override val isPublicApi: Boolean = false
-
-    override val signature: IdSignature
-        get() = error("IdSignature is allowed only for PublicApi symbols")
+    override val signature: IdSignature?
+        get() = null
 
     override val isBound: Boolean
         get() = _owner != null
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/impl/IrPublicSymbolBase.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/impl/IrPublicSymbolBase.kt
index 8113ad4db88..db54edf7a70 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/impl/IrPublicSymbolBase.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/symbols/impl/IrPublicSymbolBase.kt
@@ -52,8 +52,6 @@ abstract class IrBindablePublicSymbolBase<out D : DeclarationDescriptor, B : IrS
         }
     }
 
-    override val isPublicApi: Boolean = true
-
     override val isBound: Boolean
         get() = _owner != null
 }
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSystemContext.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSystemContext.kt
index 37851add71b..a82921a5d91 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSystemContext.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/IrTypeSystemContext.kt
@@ -345,18 +345,18 @@ interface IrTypeSystemContext : TypeSystemContext, TypeSystemCommonSuperTypesCon
     }
 
     override fun TypeConstructorMarker.getPrimitiveType(): PrimitiveType? {
-        if (this !is IrClassSymbol || !isPublicApi) return null
+        if (this !is IrClassSymbol) return null
 
-        val signature = signature.asPublic()
+        val signature = signature?.asPublic()
         if (signature == null || signature.packageFqName != "kotlin") return null
 
         return PrimitiveType.getByShortName(signature.declarationFqName)
     }
 
     override fun TypeConstructorMarker.getPrimitiveArrayType(): PrimitiveType? {
-        if (this !is IrClassSymbol || !isPublicApi) return null
+        if (this !is IrClassSymbol) return null
 
-        val signature = signature.asPublic()
+        val signature = signature?.asPublic()
         if (signature == null || signature.packageFqName != "kotlin") return null
 
         return PrimitiveType.getByShortArrayName(signature.declarationFqName)
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/irTypePredicates.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/irTypePredicates.kt
index 081e4811541..c564bbe901c 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/irTypePredicates.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/irTypePredicates.kt
@@ -57,7 +57,6 @@ fun getPublicSignature(packageFqName: FqName, name: String) =
 private fun IrType.isClassType(signature: IdSignature.PublicSignature, hasQuestionMark: Boolean? = null): Boolean {
     if (this !is IrSimpleType) return false
     if (hasQuestionMark != null && this.hasQuestionMark != hasQuestionMark) return false
-    if (!classifier.isPublicApi || !classifier.signature.isPublic) return false
     return signature == classifier.signature
 }
 
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/AdditionalIrUtils.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/AdditionalIrUtils.kt
index 92a6fcf45c9..d7431b7079f 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/AdditionalIrUtils.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/AdditionalIrUtils.kt
@@ -86,7 +86,7 @@ private val IrConstructorCall.annotationClass
     get() = this.symbol.owner.constructedClass
 
 val IrClass.packageFqName: FqName?
-    get() = if (symbol.isPublicApi) symbol.signature.packageFqName() else parent.getPackageFragment()?.fqName
+    get() = symbol.signature?.packageFqName() ?: parent.getPackageFragment()?.fqName
 
 fun IrDeclarationWithName.hasEqualFqName(fqName: FqName): Boolean =
     name == fqName.shortName() && when (val parent = parent) {
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/DeclarationStubGenerator.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/DeclarationStubGenerator.kt
index 03da280a824..2ee83228ff0 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/DeclarationStubGenerator.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/DeclarationStubGenerator.kt
@@ -77,7 +77,10 @@ class DeclarationStubGenerator(
             return generateStubBySymbol(symbol, symbol.descriptor)
         }
         val descriptor = if (symbol.descriptor is WrappedDeclarationDescriptor<*>)
-            findDescriptorBySignature(symbol.signature)
+            findDescriptorBySignature(
+                symbol.signature
+                    ?: error("Symbol is not public API. Expected signature for symbol: ${symbol.descriptor}")
+            )
         else
             symbol.descriptor
         if (descriptor == null) return null
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/SymbolTable.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/SymbolTable.kt
index 66d89e8e664..c9dd441c13e 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/SymbolTable.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/SymbolTable.kt
@@ -216,9 +216,9 @@ class SymbolTable(
         }
 
         override fun set(d: D, s: S) {
-            if (s.isPublicApi) {
-                idSigToSymbol[s.signature] = s
-            } else {
+            s.signature?.let {
+                idSigToSymbol[it] = s
+            } ?: run {
                 descriptorToSymbol[d] = s
             }
         }
@@ -264,10 +264,10 @@ class SymbolTable(
             fun getLocal(d: D) = descriptorToSymbol[d]
 
             operator fun set(d: D, s: S) {
-                if (s.isPublicApi) {
+                s.signature?.let {
                     require(d is TypeParameterDescriptor)
-                    idSigToSymbol[s.signature] = s
-                } else {
+                    idSigToSymbol[it] = s
+                } ?: run {
                     descriptorToSymbol[d] = s
                 }
             }
diff --git a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/DeclarationTable.kt b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/DeclarationTable.kt
index 85902a42361..0681c6f8fbf 100644
--- a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/DeclarationTable.kt
+++ b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/DeclarationTable.kt
@@ -36,7 +36,7 @@ abstract class GlobalDeclarationTable(
     protected fun loadKnownBuiltins(builtIns: IrBuiltIns) {
         builtIns.knownBuiltins.forEach {
             val symbol = (it as IrSymbolOwner).symbol
-            table[it] = symbol.signature.also { id -> clashTracker.commit(it, id) }
+            table[it] = symbol.signature!!.also { id -> clashTracker.commit(it, id) }
         }
     }
 
diff --git a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IncrementalCompilationSupport.kt b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IncrementalCompilationSupport.kt
index e81e0c2893e..65f286ae02a 100644
--- a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IncrementalCompilationSupport.kt
+++ b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IncrementalCompilationSupport.kt
@@ -119,7 +119,7 @@ class CurrentModuleWithICDeserializer(
         symbolTable.forEachPublicSymbol {
             if (it.descriptor.isDirtyDescriptor()) { // public && non-deserialized should be dirty symbol
                 if (it !in knownBuiltIns) {
-                    dirtyDeclarations[it.signature] = it
+                    dirtyDeclarations[it.signature!!] = it
                 }
             }
         }
diff --git a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrModuleDeserializer.kt b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrModuleDeserializer.kt
index d1b4b24e174..5a562f3a091 100644
--- a/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrModuleDeserializer.kt
+++ b/compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrModuleDeserializer.kt
@@ -37,9 +37,10 @@ abstract class IrModuleDeserializer(val moduleDescriptor: ModuleDescriptor) {
     abstract fun deserializeIrSymbol(idSig: IdSignature, symbolKind: BinarySymbolData.SymbolKind): IrSymbol
 
     open fun declareIrSymbol(symbol: IrSymbol) {
-        assert(symbol.isPublicApi) { "Symbol is not public API: ${symbol.descriptor}" }
+        val signature = symbol.signature
+        require(signature != null) { "Symbol is not public API: ${symbol.descriptor}" }
         assert(symbol.descriptor !is WrappedDeclarationDescriptor<*>)
-        deserializeIrSymbol(symbol.signature, symbol.kind())
+        deserializeIrSymbol(signature, symbol.kind())
     }
 
     open val klib: IrLibrary get() = error("Unsupported operation")
@@ -166,8 +167,9 @@ class IrModuleDeserializerWithBuiltIns(
     }
 
     override fun declareIrSymbol(symbol: IrSymbol) {
-        if (symbol.isPublicApi && checkIsFunctionInterface(symbol.signature))
-            resolveFunctionalInterface(symbol.signature, symbol.kind())
+        val signature = symbol.signature
+        if (signature != null && checkIsFunctionInterface(signature))
+            resolveFunctionalInterface(signature, symbol.kind())
         else delegate.declareIrSymbol(symbol)
     }