diff --git a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/signaturer/FirBasedSignatureComposer.kt b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/signaturer/FirBasedSignatureComposer.kt
index d2724e1af13..6636dec68ce 100644
--- a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/signaturer/FirBasedSignatureComposer.kt
+++ b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/signaturer/FirBasedSignatureComposer.kt
@@ -18,6 +18,7 @@ import org.jetbrains.kotlin.fir.declarations.utils.visibility
 import org.jetbrains.kotlin.fir.symbols.ConeClassLikeLookupTag
 import org.jetbrains.kotlin.fir.visitors.FirVisitor
 import org.jetbrains.kotlin.ir.util.IdSignature
+import org.jetbrains.kotlin.name.FqName
 
 // @NoMutableState -- we'll restore this annotation once we get rid of withFileSignature().
 class FirBasedSignatureComposer(override val mangler: FirMangler) : Fir2IrSignatureComposer {
@@ -122,7 +123,7 @@ class FirBasedSignatureComposer(override val mangler: FirMangler) : Fir2IrSignat
             else -> error("Unsupported FIR declaration in signature composer: ${declaration.render()}")
         }
         return if (isTopLevelPrivate(declaration) || forceTopLevelPrivate) {
-            val fileSig = fileSignature ?: return null
+            val fileSig = fileSignature ?: declaration.fakeFileSignature(publicSignature)
             IdSignature.CompositeSignature(fileSig, publicSignature)
         } else
             publicSignature
@@ -181,6 +182,13 @@ class FirBasedSignatureComposer(override val mangler: FirMangler) : Fir2IrSignat
     private fun isTopLevelPrivate(declaration: FirDeclaration): Boolean =
         declaration.symbol.getOwnerLookupTag() == null && declaration is FirMemberDeclaration && declaration.visibility == Visibilities.Private
 
+    // We only need file signatures to distinguish between declarations with the same fqName across different files,
+    // so FirDeclaration itself is an appropriate id.
+    private fun FirDeclaration.fakeFileSignature(commonSignature: IdSignature.CommonSignature) =
+        IdSignature.FileSignature(
+            this, FqName(commonSignature.packageFqName + "." + commonSignature.declarationFqName), "<unknown>"
+        )
+
     private fun FirProperty.getterOrDefault() =
         getter ?: FirDefaultPropertyGetter(
             source = null,
diff --git a/compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java b/compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java
index 56dfa2e8fc8..ef104a873fb 100644
--- a/compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java
+++ b/compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java
@@ -7415,6 +7415,12 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
             runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/platformTypes.kt");
         }
 
+        @Test
+        @TestMetadata("privateSuperType.kt")
+        public void testPrivateSuperType() throws Exception {
+            runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt");
+        }
+
         @Test
         @TestMetadata("propertyReference.kt")
         public void testPropertyReference() throws Exception {
diff --git a/compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt b/compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt
new file mode 100644
index 00000000000..0b2ed182583
--- /dev/null
+++ b/compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt
@@ -0,0 +1,19 @@
+// MODULE: lib
+// FILE: Z.kt
+package z
+
+private interface I {
+     fun k() = "K"
+}
+
+interface G<T>
+
+class Z : I, G<I> {
+    val o = "O"
+}
+
+// MODULE: main(lib)
+// FILE: box.kt
+import z.Z
+
+fun box() = Z().run { o + k() }
\ No newline at end of file
diff --git a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java
index 7756305fd70..dd0d83d0112 100644
--- a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java
+++ b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java
@@ -7301,6 +7301,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/platformTypes.kt");
         }
 
+        @Test
+        @TestMetadata("privateSuperType.kt")
+        public void testPrivateSuperType() throws Exception {
+            runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt");
+        }
+
         @Test
         @TestMetadata("propertyReference.kt")
         public void testPropertyReference() throws Exception {
diff --git a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java
index 427d04aba2c..da89d534886 100644
--- a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java
+++ b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java
@@ -7415,6 +7415,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/platformTypes.kt");
         }
 
+        @Test
+        @TestMetadata("privateSuperType.kt")
+        public void testPrivateSuperType() throws Exception {
+            runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt");
+        }
+
         @Test
         @TestMetadata("propertyReference.kt")
         public void testPropertyReference() throws Exception {
diff --git a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/JvmIrAgainstOldBoxTestGenerated.java b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/JvmIrAgainstOldBoxTestGenerated.java
index 3ac7275c4fa..5f73f211f15 100644
--- a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/JvmIrAgainstOldBoxTestGenerated.java
+++ b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/JvmIrAgainstOldBoxTestGenerated.java
@@ -397,6 +397,12 @@ public class JvmIrAgainstOldBoxTestGenerated extends AbstractJvmIrAgainstOldBoxT
         runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/platformTypes.kt");
     }
 
+    @Test
+    @TestMetadata("privateSuperType.kt")
+    public void testPrivateSuperType() throws Exception {
+        runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt");
+    }
+
     @Test
     @TestMetadata("propertyReference.kt")
     public void testPropertyReference() throws Exception {
diff --git a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/JvmOldAgainstIrBoxTestGenerated.java b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/JvmOldAgainstIrBoxTestGenerated.java
index 4ddfad88c42..9377b0ebc61 100644
--- a/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/JvmOldAgainstIrBoxTestGenerated.java
+++ b/compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/JvmOldAgainstIrBoxTestGenerated.java
@@ -397,6 +397,12 @@ public class JvmOldAgainstIrBoxTestGenerated extends AbstractJvmOldAgainstIrBoxT
         runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/platformTypes.kt");
     }
 
+    @Test
+    @TestMetadata("privateSuperType.kt")
+    public void testPrivateSuperType() throws Exception {
+        runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt");
+    }
+
     @Test
     @TestMetadata("propertyReference.kt")
     public void testPropertyReference() throws Exception {
diff --git a/native/native.tests/tests-gen/org/jetbrains/kotlin/konan/blackboxtest/NativeCodegenBoxTestGenerated.java b/native/native.tests/tests-gen/org/jetbrains/kotlin/konan/blackboxtest/NativeCodegenBoxTestGenerated.java
index 23eb534de27..0d6ba4d6336 100644
--- a/native/native.tests/tests-gen/org/jetbrains/kotlin/konan/blackboxtest/NativeCodegenBoxTestGenerated.java
+++ b/native/native.tests/tests-gen/org/jetbrains/kotlin/konan/blackboxtest/NativeCodegenBoxTestGenerated.java
@@ -5605,6 +5605,12 @@ public class NativeCodegenBoxTestGenerated extends AbstractNativeCodegenBoxTest
                 runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/nestedTypeAliasExpansion.kt");
             }
 
+            @Test
+            @TestMetadata("privateSuperType.kt")
+            public void testPrivateSuperType() throws Exception {
+                runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/privateSuperType.kt");
+            }
+
             @Test
             @TestMetadata("propertyReference.kt")
             public void testPropertyReference() throws Exception {