diff --git a/compiler/fir/fir-deserialization/src/org/jetbrains/kotlin/fir/deserialization/ClassDeserialization.kt b/compiler/fir/fir-deserialization/src/org/jetbrains/kotlin/fir/deserialization/ClassDeserialization.kt
index ed9ba797e4c..5f9a05f3bba 100644
--- a/compiler/fir/fir-deserialization/src/org/jetbrains/kotlin/fir/deserialization/ClassDeserialization.kt
+++ b/compiler/fir/fir-deserialization/src/org/jetbrains/kotlin/fir/deserialization/ClassDeserialization.kt
@@ -215,7 +215,9 @@ fun deserializeClassToSymbol(
 
         it.sourceElement = containerSource
 
-        it.proto = FirClassProto(classProto, nameResolver)
+        classProto.getExtensionOrNull(JvmProtoBuf.classModuleName)?.let { idx ->
+            it.moduleName = nameResolver.getString(idx)
+        }
     }
 }
 
diff --git a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazyClass.kt b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazyClass.kt
index 98cdecfa9fc..8d7ad652134 100644
--- a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazyClass.kt
+++ b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazyClass.kt
@@ -28,8 +28,6 @@ import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.impl.IrSimpleTypeImpl
 import org.jetbrains.kotlin.ir.util.isFakeOverride
 import org.jetbrains.kotlin.ir.util.render
-import org.jetbrains.kotlin.metadata.ProtoBuf
-import org.jetbrains.kotlin.metadata.deserialization.NameResolver
 import org.jetbrains.kotlin.name.Name
 
 class Fir2IrLazyClass(
@@ -204,11 +202,8 @@ class Fir2IrLazyClass(
         get() = null
         set(_) = error("We should never need to store metadata of external declarations.")
 
-    override val classProto: ProtoBuf.Class?
-        get() = fir.proto?.classProto
-
-    override val nameResolver: NameResolver?
-        get() = fir.proto?.nameResolver
+    override val moduleName: String?
+        get() = fir.moduleName
 
     private fun FirNamedFunctionSymbol.isAbstractMethodOfAny(): Boolean {
         val fir = fir
diff --git a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/FirDeclarationUtil.kt b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/FirDeclarationUtil.kt
index b3f8e82e51f..03a7517ab73 100644
--- a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/FirDeclarationUtil.kt
+++ b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/FirDeclarationUtil.kt
@@ -184,11 +184,9 @@ private object SourceElementKey : FirDeclarationDataKey()
 
 var FirRegularClass.sourceElement: SourceElement? by FirDeclarationDataRegistry.data(SourceElementKey)
 
-private object ClassProtoKey : FirDeclarationDataKey()
+private object ModuleNameKey : FirDeclarationDataKey()
 
-class FirClassProto(val classProto: ProtoBuf.Class, val nameResolver: NameResolver)
-
-var FirRegularClass.proto: FirClassProto? by FirDeclarationDataRegistry.data(ClassProtoKey)
+var FirRegularClass.moduleName: String? by FirDeclarationDataRegistry.data(ModuleNameKey)
 
 var FirTypeAlias.sourceElement: SourceElement? by FirDeclarationDataRegistry.data(SourceElementKey)
 
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 44ca1435ed9..6511835ba7d 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
@@ -499,13 +499,15 @@ class MethodSignatureMapper(private val context: JvmBackendContext) {
         var current: IrDeclarationParent? = function.parent
         while (current != null) {
             when (current) {
-                is IrMaybeDeserializedClass -> {
+                is IrLazyClass -> {
                     val classProto = current.classProto ?: return null
                     val nameResolver = current.nameResolver ?: return null
                     return classProto.getExtensionOrNull(JvmProtoBuf.classModuleName)
                         ?.let(nameResolver::getString)
                         ?: JvmProtoBufUtil.DEFAULT_MODULE_NAME
                 }
+                is IrMaybeDeserializedClass ->
+                    return current.moduleName
                 is IrExternalPackageFragment -> {
                     val source = current.containerSource ?: return null
                     return (source as? JvmPackagePartSource)?.moduleName
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 1f3a4b46274..47157ee4145 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
@@ -40,7 +40,7 @@ class IrLazyClass(
     override val isFun: Boolean,
     override val stubGenerator: DeclarationStubGenerator,
     override val typeTranslator: TypeTranslator
-) : IrClass(), IrLazyDeclarationBase, IrMaybeDeserializedClass {
+) : IrClass(), IrLazyDeclarationBase {
     init {
         symbol.bind(this)
     }
@@ -103,8 +103,8 @@ class IrLazyClass(
 
     override var attributeOwnerId: IrAttributeContainer = this
 
-    override val classProto: ProtoBuf.Class? get() = (descriptor as? DeserializedClassDescriptor)?.classProto
-    override val nameResolver: NameResolver? get() = (descriptor as? DeserializedClassDescriptor)?.c?.nameResolver
+    val classProto: ProtoBuf.Class? get() = (descriptor as? DeserializedClassDescriptor)?.classProto
+    val nameResolver: NameResolver? get() = (descriptor as? DeserializedClassDescriptor)?.c?.nameResolver
     override val source: SourceElement get() = descriptor.source
 
     override var metadata: MetadataSource?
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrMaybeDeserializedClass.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrMaybeDeserializedClass.kt
index 140fc81e159..6ce2e70899a 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrMaybeDeserializedClass.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrMaybeDeserializedClass.kt
@@ -6,10 +6,7 @@
 package org.jetbrains.kotlin.ir.declarations.lazy
 
 import org.jetbrains.kotlin.ir.declarations.IrDeclaration
-import org.jetbrains.kotlin.metadata.ProtoBuf
-import org.jetbrains.kotlin.metadata.deserialization.NameResolver
 
 interface IrMaybeDeserializedClass : IrDeclaration {
-    val classProto: ProtoBuf.Class?
-    val nameResolver: NameResolver?
+    val moduleName: String?
 }
\ No newline at end of file