diff --git a/include/pocketpy/interpreter/frame.h b/include/pocketpy/interpreter/frame.h
index deb3f895..2c7e1f68 100644
--- a/include/pocketpy/interpreter/frame.h
+++ b/include/pocketpy/interpreter/frame.h
@@ -60,6 +60,5 @@ void Frame__prepare_jump_break(Frame* self, ValueStack*, int);
 int Frame__prepare_loop_break(Frame* self, ValueStack*);
 int Frame__exit_block(Frame* self, ValueStack*, int);
 
-void Frame__gc_mark(Frame* self);
 UnwindTarget* Frame__find_unwind_target(Frame* self, int iblock);
 void Frame__set_unwind_target(Frame* self, py_TValue* sp);