diff --git a/include/pocketpy/vm.h b/include/pocketpy/vm.h
index fd10974a..fd7a9c5d 100644
--- a/include/pocketpy/vm.h
+++ b/include/pocketpy/vm.h
@@ -465,7 +465,7 @@ public:
     void delattr(PyObject* obj, StrName name);
     PyObject* get_unbound_method(PyObject* obj, StrName name, PyObject** self, bool throw_err=true, bool fallback=false);
     void parse_int_slice(const Slice& s, int length, int& start, int& stop, int& step);
-    PyObject* format(Str, PyObject*);
+    PyObject* _format_string(Str, PyObject*);
     void setattr(PyObject* obj, StrName name, PyObject* value);
     template<int ARGC>
     PyObject* bind_method(PyObject*, Str, NativeFuncC);
diff --git a/src/ceval.cpp b/src/ceval.cpp
index d323a3ef..3c709f6f 100644
--- a/src/ceval.cpp
+++ b/src/ceval.cpp
@@ -805,7 +805,7 @@ __NEXT_STEP:;
     TARGET(FORMAT_STRING) {
         PyObject* _0 = POPX();
         const Str& spec = CAST(Str&, co_consts[byte.arg]);
-        PUSH(format(spec, _0));
+        PUSH(_format_string(spec, _0));
     } DISPATCH();
     /*****************************************/
     TARGET(INC_FAST){
diff --git a/src/vm.cpp b/src/vm.cpp
index 70f41a6e..5c7978ab 100644
--- a/src/vm.cpp
+++ b/src/vm.cpp
@@ -475,7 +475,7 @@ i64 VM::py_hash(PyObject* obj){
     }
 }
 
-PyObject* VM::format(Str spec, PyObject* obj){
+PyObject* VM::_format_string(Str spec, PyObject* obj){
     if(spec.empty()) return py_str(obj);
     char type;
     switch(spec.end()[-1]){