diff --git a/ets2panda/compiler/core/ETSemitter.cpp b/ets2panda/compiler/core/ETSemitter.cpp
index 3e6f38dbad8fa784e298f4348bcfddff21217661..6b02a7ef3257f6574fdcc74df094f23f904a60f3 100644
--- a/ets2panda/compiler/core/ETSemitter.cpp
+++ b/ets2panda/compiler/core/ETSemitter.cpp
@@ -136,6 +136,9 @@ static pandasm::Function GenScriptFunction(const ir::ScriptFunction *scriptFunc,
 
     if (scriptFunc->IsConstructor() || scriptFunc->IsStaticBlock()) {
         func.returnType = pandasm::Type(Signatures::PRIMITIVE_VOID, 0);
+    } else if (scriptFunc->Signature()->HasSignatureFlag(checker::SignatureFlags::THIS_RETURN_TYPE) &&
+               scriptFunc->Signature()->HasSignatureFlag(checker::SignatureFlags::EXTENSION_FUNCTION)) {
+        func.returnType = PandasmTypeWithRank(paramScope->Params()[0]->TsType());
     } else {
         func.returnType = PandasmTypeWithRank(scriptFunc->Signature()->ReturnType());
     }