diff --git a/vm_core.h b/vm_core.h
index 479698932e..1ebcea7a2d 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -1624,7 +1624,11 @@ VALUE rb_proc_dup(VALUE self);
 /* for debug */
 extern void rb_vmdebug_stack_dump_raw(const rb_execution_context_t *ec, const rb_control_frame_t *cfp);
 extern void rb_vmdebug_debug_print_pre(const rb_execution_context_t *ec, const rb_control_frame_t *cfp, const VALUE *_pc);
-extern void rb_vmdebug_debug_print_post(const rb_execution_context_t *ec, const rb_control_frame_t *cfp);
+extern void rb_vmdebug_debug_print_post(const rb_execution_context_t *ec, const rb_control_frame_t *cfp
+#if OPT_STACK_CACHING
+    , VALUE reg_a, VALUE reg_b
+#endif
+);
 
 #define SDR() rb_vmdebug_stack_dump_raw(GET_EC(), GET_EC()->cfp)
 #define SDR2(cfp) rb_vmdebug_stack_dump_raw(GET_EC(), (cfp))