diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/MethodSignatureMapper.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/MethodSignatureMapper.kt
index 24c660fafa6..27e138827d2 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/MethodSignatureMapper.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/MethodSignatureMapper.kt
@@ -39,7 +39,6 @@ import org.jetbrains.kotlin.load.java.getOverriddenBuiltinReflectingJvmDescripto
 import org.jetbrains.kotlin.load.kotlin.TypeMappingMode
 import org.jetbrains.kotlin.load.kotlin.forceSingleValueParameterBoxing
 import org.jetbrains.kotlin.load.kotlin.getJvmModuleNameForDeserializedDescriptor
-import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.jvm.jvmSignature.JvmMethodGenericSignature
 import org.jetbrains.kotlin.resolve.jvm.jvmSignature.JvmMethodParameterKind
 import org.jetbrains.kotlin.resolve.jvm.jvmSignature.JvmMethodSignature
@@ -105,7 +104,7 @@ class MethodSignatureMapper(private val context: JvmBackendContext) {
 
         if (function.isTopLevel) {
             if (Visibilities.isPrivate(function.visibility) && newName != "<clinit>" &&
-                function.parentAsClass.attributeOwnerId in context.multifileFacadeForPart
+                (function.parent as? IrClass)?.attributeOwnerId in context.multifileFacadeForPart
             ) {
                 return "$newName$${function.parentAsClass.name.asString()}"
             }
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/GenerateMultifileFacades.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/GenerateMultifileFacades.kt
index 80df12a24ed..99d4b85e17c 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/GenerateMultifileFacades.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/GenerateMultifileFacades.kt
@@ -129,6 +129,7 @@ private fun generateMultifileFacades(
         }.apply {
             parent = file
             createImplicitParameterDeclarationWithWrappedDescriptor()
+            origin = IrDeclarationOrigin.FILE_CLASS
             if (jvmClassName.packageFqName != kotlinPackageFqName) {
                 context.classNameOverride[this] = jvmClassName
             }
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 327f6e207a2..a5f2afd82ba 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
@@ -12,7 +12,6 @@ import org.jetbrains.kotlin.descriptors.annotations.Annotations
 import org.jetbrains.kotlin.descriptors.impl.TypeAliasConstructorDescriptor
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.*
-import org.jetbrains.kotlin.ir.descriptors.IrBasedDeclarationDescriptor
 import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.types.classifierOrFail
 import org.jetbrains.kotlin.ir.types.toKotlinType
@@ -1056,11 +1055,12 @@ open class WrappedFieldDescriptor(
 
 private fun getContainingDeclaration(declaration: IrDeclarationWithName): DeclarationDescriptor {
     val parent = declaration.parent
-    return if (parent is IrClass && parent.origin == IrDeclarationOrigin.FILE_CLASS && parent.parent is IrExternalPackageFragment) {
-        // JVM IR adds facade classes for IR of functions/properties loaded from dependencies. However, these shouldn't exist
-        // in the descriptor hierarchy, since this is what the old backend (dealing with descriptors) expects.
-        return (parent.parent as IrExternalPackageFragment).packageFragmentDescriptor
+    val parentDescriptor = (parent as IrSymbolOwner).symbol.descriptor
+    return if (parent is IrClass && parent.origin == IrDeclarationOrigin.FILE_CLASS) {
+        // JVM IR adds facade classes for IR of functions/properties loaded both from sources and dependencies. However, these shouldn't
+        // exist in the descriptor hierarchy, since this is what the old backend (dealing with descriptors) expects.
+        parentDescriptor.containingDeclaration!!
     } else {
-        (parent as IrSymbolOwner).symbol.descriptor
+        parentDescriptor
     }
 }
diff --git a/compiler/testData/codegen/box/multifileClasses/optimized/internalFunction.kt b/compiler/testData/codegen/box/multifileClasses/optimized/internalFunction.kt
new file mode 100644
index 00000000000..69d159e1929
--- /dev/null
+++ b/compiler/testData/codegen/box/multifileClasses/optimized/internalFunction.kt
@@ -0,0 +1,19 @@
+// TARGET_BACKEND: JVM
+// IGNORE_LIGHT_ANALYSIS
+// WITH_RUNTIME
+// !INHERIT_MULTIFILE_PARTS
+
+// FILE: test.kt
+
+@file:JvmMultifileClass
+@file:JvmName("Test")
+
+internal fun <T> List<T>.first(): T = get(0)
+
+fun test(): String {
+    return listOf("OK").first()
+}
+
+// FILE: box.kt
+
+fun box(): String = test()
diff --git a/compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java b/compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java
index 28f05f53ea9..9a85d0330ee 100644
--- a/compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java
+++ b/compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java
@@ -16517,6 +16517,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
                 runTest("compiler/testData/codegen/box/multifileClasses/optimized/calls.kt");
             }
 
+            @TestMetadata("internalFunction.kt")
+            public void testInternalFunction() throws Exception {
+                runTest("compiler/testData/codegen/box/multifileClasses/optimized/internalFunction.kt");
+            }
+
             @TestMetadata("overlappingFuns.kt")
             public void testOverlappingFuns() throws Exception {
                 runTest("compiler/testData/codegen/box/multifileClasses/optimized/overlappingFuns.kt");
diff --git a/compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java b/compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java
index 7a68adf29da..426dda2d402 100644
--- a/compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java
+++ b/compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java
@@ -16517,6 +16517,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
                 runTest("compiler/testData/codegen/box/multifileClasses/optimized/calls.kt");
             }
 
+            @TestMetadata("internalFunction.kt")
+            public void testInternalFunction() throws Exception {
+                runTest("compiler/testData/codegen/box/multifileClasses/optimized/internalFunction.kt");
+            }
+
             @TestMetadata("overlappingFuns.kt")
             public void testOverlappingFuns() throws Exception {
                 runTest("compiler/testData/codegen/box/multifileClasses/optimized/overlappingFuns.kt");
diff --git a/compiler/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java b/compiler/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java
index 5b1eb2abe52..23d3379c3c4 100644
--- a/compiler/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java
+++ b/compiler/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java
@@ -15392,6 +15392,11 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
                 runTest("compiler/testData/codegen/box/multifileClasses/optimized/calls.kt");
             }
 
+            @TestMetadata("internalFunction.kt")
+            public void testInternalFunction() throws Exception {
+                runTest("compiler/testData/codegen/box/multifileClasses/optimized/internalFunction.kt");
+            }
+
             @TestMetadata("overlappingFuns.kt")
             public void testOverlappingFuns() throws Exception {
                 runTest("compiler/testData/codegen/box/multifileClasses/optimized/overlappingFuns.kt");