diff --git a/es2panda/compiler/core/function.cpp b/es2panda/compiler/core/function.cpp
index 98ec8de00793e16be310cc846cbb38edcf3ed877..4e73c94330ee3b892d366ee837e4a37c0c7b7a73 100644
--- a/es2panda/compiler/core/function.cpp
+++ b/es2panda/compiler/core/function.cpp
@@ -171,8 +171,11 @@ static void CompileClassInitializer(PandaGen *pg, const ir::ScriptFunction *decl
 
     RegScope rs(pg);
     auto thisReg = pg->AllocReg();
+    pg->SetSourceLocationFlag(lexer::SourceLocationFlag::INVALID_SOURCE_LOCATION);
     pg->GetThis(decl);
     pg->StoreAccumulator(decl, thisReg);
+    pg->SetSourceLocationFlag(lexer::SourceLocationFlag::VALID_SOURCE_LOCATION);
+
     auto [level, slot] = pg->Scope()->Find(nullptr, true);
 
     if (!isStatic && classDef->HasInstancePrivateMethod()) {
@@ -219,12 +222,14 @@ static void CompileFunction(PandaGen *pg)
             RegScope rs(pg);
             auto thisReg = pg->AllocReg();
 
+            pg->SetSourceLocationFlag(lexer::SourceLocationFlag::INVALID_SOURCE_LOCATION);
             pg->GetThis(decl);
             pg->StoreAccumulator(decl, thisReg);
 
             auto [level, slot] = pg->Scope()->Find(classDef->InstanceInitializer()->Key());
             pg->LoadLexicalVar(decl, level, slot);
             pg->CallInit(decl, thisReg);
+            pg->SetSourceLocationFlag(lexer::SourceLocationFlag::VALID_SOURCE_LOCATION);
         }
     }
 
diff --git a/es2panda/compiler/function/functionBuilder.cpp b/es2panda/compiler/function/functionBuilder.cpp
index fda570ed4f975e4259a2850f25e0b0e43bcf32d2..f49ff4c05286c1d96b0d908ef9ae5aef3e9d6db7 100644
--- a/es2panda/compiler/function/functionBuilder.cpp
+++ b/es2panda/compiler/function/functionBuilder.cpp
@@ -50,8 +50,18 @@ void FunctionBuilder::ImplicitReturn(const ir::AstNode *node) const
         }
         pg_->LoadConst(node, Constant::JS_UNDEFINED);
         pg_->NotifyConcurrentResult(node);
-        pg_->SetSourceLocationFlag(lexer::SourceLocationFlag::VALID_SOURCE_LOCATION);
-        pg_->EmitReturnUndefined(node);
+
+        // When no source location exists (e.g., in 'instance_initializer'), mark returnundefined as INVALID.
+        bool isEmptyRange = (node->Range().start.line == 0 && node->Range().end.line == 0 &&
+                             node->Range().start.index == 0 && node->Range().end.index == 0);
+
+        if (isEmptyRange) {
+            pg_->EmitReturnUndefined(node);
+            pg_->SetSourceLocationFlag(lexer::SourceLocationFlag::VALID_SOURCE_LOCATION);
+        } else {
+            pg_->SetSourceLocationFlag(lexer::SourceLocationFlag::VALID_SOURCE_LOCATION);
+            pg_->EmitReturnUndefined(node);
+        }
         return;
     }