diff --git a/include/pocketpy/frame.h b/include/pocketpy/frame.h
index 12e51651..77b01bb2 100644
--- a/include/pocketpy/frame.h
+++ b/include/pocketpy/frame.h
@@ -94,10 +94,10 @@ struct Frame {
     Frame(PyVar* p0, const CodeObject_& co, PyVar _module)
             : _ip(-1), _next_ip(0), _sp_base(p0), co(co.get()), _module(_module), _callable(nullptr), _locals(co.get(), p0) {}
 
-    Bytecode next_bytecode() {
+    int next_bytecode() {
         _ip = _next_ip++;
         PK_DEBUG_ASSERT(_ip >= 0 && _ip < co->codes.size());
-        return co->codes[_ip];
+        return _ip;
     }
 
     PyVar* actual_sp_base() const { return _locals.a; }
diff --git a/src/ceval.cpp b/src/ceval.cpp
index fd8fc2ba..a76f97cd 100644
--- a/src/ceval.cpp
+++ b/src/ceval.cpp
@@ -111,10 +111,11 @@ PyVar VM::__run_top_frame(){
 
 __NEXT_FRAME:
     const CodeObject* co = frame->co;
+    const Bytecode* co_codes = co->codes.data();
     Bytecode byte;
 
 __NEXT_STEP:;
-    byte = frame->next_bytecode();
+    byte = co_codes[frame->next_bytecode()];
     CEVAL_STEP_CALLBACK();
 
 #if PK_DEBUG_CEVAL_STEP