diff --git a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/ConversionUtils.kt b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/ConversionUtils.kt
index 789d30bbac6..bce82b01bed 100644
--- a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/ConversionUtils.kt
+++ b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/ConversionUtils.kt
@@ -78,6 +78,10 @@ fun AbstractKtSourceElement?.startOffsetSkippingComments(): Int? {
     }
 }
 
+internal inline fun <T : IrElement> FirElement.convertWithOffsets(defaultOffset: Int, f: (startOffset: Int, endOffset: Int) -> T): T {
+    return source.convertWithOffsets(defaultOffset, f)
+}
+
 internal inline fun <T : IrElement> FirElement.convertWithOffsets(f: (startOffset: Int, endOffset: Int) -> T): T {
     return source.convertWithOffsets(f)
 }
@@ -89,15 +93,19 @@ internal fun <T : IrElement> FirPropertyAccessor?.convertWithOffsets(
 }
 
 internal inline fun <T : IrElement> KtSourceElement?.convertWithOffsets(f: (startOffset: Int, endOffset: Int) -> T): T {
+    return convertWithOffsets(UNDEFINED_OFFSET, f)
+}
+
+internal inline fun <T : IrElement> KtSourceElement?.convertWithOffsets(defaultOffset: Int, f: (startOffset: Int, endOffset: Int) -> T): T {
     val startOffset: Int
     val endOffset: Int
 
     if (isCompiledElement(psi) || this?.kind == KtFakeSourceElementKind.DataClassGeneratedMembers) {
-        startOffset = UNDEFINED_OFFSET
-        endOffset = UNDEFINED_OFFSET
+        startOffset = defaultOffset
+        endOffset = defaultOffset
     } else {
-        startOffset = this?.startOffsetSkippingComments() ?: this?.startOffset ?: UNDEFINED_OFFSET
-        endOffset = this?.endOffset ?: UNDEFINED_OFFSET
+        startOffset = this?.startOffsetSkippingComments() ?: this?.startOffset ?: defaultOffset
+        endOffset = this?.endOffset ?: defaultOffset
     }
 
     return f(startOffset, endOffset)
diff --git a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/DataClassMembersGenerator.kt b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/DataClassMembersGenerator.kt
index 8bdee57aba5..ba15075b00c 100644
--- a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/DataClassMembersGenerator.kt
+++ b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/DataClassMembersGenerator.kt
@@ -21,7 +21,6 @@ import org.jetbrains.kotlin.fir.scopes.getProperties
 import org.jetbrains.kotlin.fir.symbols.impl.FirNamedFunctionSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
 import org.jetbrains.kotlin.fir.types.*
-import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
 import org.jetbrains.kotlin.ir.builders.IrGeneratorContextBase
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.IrMemberAccessExpression
@@ -193,8 +192,8 @@ class DataClassMembersGenerator(val components: Fir2IrComponents) : Fir2IrCompon
             irFunction.declareThisReceiverParameter(
                 irClass.defaultType,
                 IrDeclarationOrigin.DEFINED,
-                UNDEFINED_OFFSET,
-                UNDEFINED_OFFSET
+                SYNTHETIC_OFFSET,
+                SYNTHETIC_OFFSET
             )
 
         fun generateHeaders(): List<FirDeclaration> {
@@ -313,8 +312,8 @@ class DataClassMembersGenerator(val components: Fir2IrComponents) : Fir2IrCompon
             val signature = if (klass.symbol.classId.isLocal) null else components.signatureComposer.composeSignature(syntheticCounterpart)
             val symbol = components.declarationStorage.createFunctionSymbol(signature)
             return components.irFactory.createSimpleFunction(
-                startOffset = UNDEFINED_OFFSET,
-                endOffset = UNDEFINED_OFFSET,
+                startOffset = SYNTHETIC_OFFSET,
+                endOffset = SYNTHETIC_OFFSET,
                 origin = origin,
                 name = name,
                 visibility = DescriptorVisibilities.PUBLIC,
@@ -351,8 +350,8 @@ class DataClassMembersGenerator(val components: Fir2IrComponents) : Fir2IrCompon
 
         private fun createSyntheticIrParameter(irFunction: IrFunction, name: Name, type: IrType, index: Int = 0): IrValueParameter =
             components.irFactory.createValueParameter(
-                startOffset = UNDEFINED_OFFSET,
-                endOffset = UNDEFINED_OFFSET,
+                startOffset = SYNTHETIC_OFFSET,
+                endOffset = SYNTHETIC_OFFSET,
                 origin = IrDeclarationOrigin.DEFINED,
                 name = name,
                 type = type,
diff --git a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/Fir2IrCallableDeclarationsGenerator.kt b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/Fir2IrCallableDeclarationsGenerator.kt
index a919f75306b..6be2fa904fd 100644
--- a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/Fir2IrCallableDeclarationsGenerator.kt
+++ b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/Fir2IrCallableDeclarationsGenerator.kt
@@ -111,11 +111,16 @@ class Fir2IrCallableDeclarationsGenerator(val components: Fir2IrComponents) : Fi
             @Suppress("USELESS_CAST") // K2 warning suppression, TODO: KT-62472
             if (isLambda) ((function as FirAnonymousFunction).typeRef as? FirResolvedTypeRef)?.type?.isSuspendOrKSuspendFunctionType(session) == true
             else function.isSuspend
-        val created = function.convertWithOffsets { startOffset, endOffset ->
+        val defaultOffset = when {
+            function.origin == FirDeclarationOrigin.Synthetic.DataClassMember -> SYNTHETIC_OFFSET
+            updatedOrigin == IrDeclarationOrigin.DELEGATED_MEMBER -> SYNTHETIC_OFFSET
+            else -> UNDEFINED_OFFSET
+        }
+        val created = function.convertWithOffsets(defaultOffset) { startOffset, endOffset ->
             classifierStorage.preCacheTypeParameters(function, symbol)
             irFactory.createSimpleFunction(
-                startOffset = if (updatedOrigin == IrDeclarationOrigin.DELEGATED_MEMBER) SYNTHETIC_OFFSET else startOffset,
-                endOffset = if (updatedOrigin == IrDeclarationOrigin.DELEGATED_MEMBER) SYNTHETIC_OFFSET else endOffset,
+                startOffset = startOffset,
+                endOffset = endOffset,
                 origin = updatedOrigin,
                 name = name,
                 visibility = components.visibilityConverter.convertToDescriptorVisibility(visibility),
diff --git a/compiler/testData/debug/stepping/dataClass.kt b/compiler/testData/debug/stepping/dataClass.kt
index 7a4586fc0e1..861710bd054 100644
--- a/compiler/testData/debug/stepping/dataClass.kt
+++ b/compiler/testData/debug/stepping/dataClass.kt
@@ -61,7 +61,7 @@ fun box() {
 // test.kt:25 box
 // test.kt:26 box
 
-// EXPECTATIONS ClassicFrontend JS_IR
+// EXPECTATIONS JS_IR
 // test.kt:14 box
 // test.kt:4 <init>
 // test.kt:4 <init>
@@ -118,63 +118,6 @@ fun box() {
 // test.kt:6 <init>
 // test.kt:26 box
 
-// EXPECTATIONS FIR JS_IR // TODO: There is an inconsistency in names between K1 and K2. This should be fixed in KT-64435.
-// test.kt:14 box
-// test.kt:4 <init>
-// test.kt:4 <init>
-// test.kt:4 <init>
-// test.kt:15 box
-// test.kt:4 <init>
-// test.kt:4 <init>
-// test.kt:4 <init>
-// test.kt:15 box
-// test.kt:1 protoOf.equals
-// test.kt:1 protoOf.equals
-// test.kt:1 protoOf.equals
-// test.kt:1 protoOf.equals
-// test.kt:1 protoOf.equals
-// test.kt:1 protoOf.equals
-// test.kt:16 box
-// test.kt:1 protoOf.hashCode
-// test.kt:1 protoOf.hashCode
-// test.kt:17 box
-// test.kt:1 protoOf.toString
-// test.kt:18 box
-// test.kt:1 protoOf.component1_7eebsc_k$
-// test.kt:18 box
-// test.kt:1 protoOf.component2_7eebsb_k$
-// test.kt:19 box
-// test.kt:1 protoOf.copy$default_8mg6yi_k$
-// test.kt:1 protoOf.copy$default_8mg6yi_k$
-// test.kt:1 protoOf.copy_xhhsuv_k$
-// test.kt:4 <init>
-// test.kt:4 <init>
-// test.kt:4 <init>
-// test.kt:20 box
-// test.kt:6 <init>
-// test.kt:6 <init>
-// test.kt:6 <init>
-// test.kt:21 box
-// test.kt:6 <init>
-// test.kt:6 <init>
-// test.kt:6 <init>
-// test.kt:21 box
-// test.kt:8 equals
-// test.kt:22 box
-// test.kt:9 hashCode
-// test.kt:23 box
-// test.kt:7 toString
-// test.kt:24 box
-// test.kt:1 protoOf.component1_7eebsc_k$
-// test.kt:24 box
-// test.kt:1 protoOf.component2_7eebsb_k$
-// test.kt:25 box
-// test.kt:10 copy
-// test.kt:6 <init>
-// test.kt:6 <init>
-// test.kt:6 <init>
-// test.kt:26 box
-
 // EXPECTATIONS WASM
 // test.kt:14 $box (12, 14, 18, 18, 18, 18, 12)
 // String.kt:141 $kotlin.stringLiteral (17, 28, 17, 17, 28, 17, 17, 28, 17, 17, 28, 17, 17, 28, 17, 17, 28, 17, 17, 28, 17, 17, 28, 17, 17, 28, 17, 17, 28, 17, 17, 28, 17, 17, 28, 17, 17, 28, 17)
diff --git a/compiler/testData/debug/stepping/delegation.kt b/compiler/testData/debug/stepping/delegation.kt
index b7f0fad4daf..471fc3a71bb 100644
--- a/compiler/testData/debug/stepping/delegation.kt
+++ b/compiler/testData/debug/stepping/delegation.kt
@@ -23,6 +23,13 @@ fun box() {
 // test.kt:14 <init>
 // test.kt:17 box
 // test.kt:18 box
+// EXPECTATIONS FIR JVM_IR
+// test.kt:14 f
+// test.kt:10 f
+// test.kt:11 f
+// test.kt:14 f
+// test.kt:19 box
+// EXPECTATIONS ClassicFrontend JVM_IR
 // test.kt:11 f
 // test.kt:-1 f
 // test.kt:19 box