diff --git a/method.h b/method.h
index 8328b86ee96102..9e2fd249683c0c 100644
--- a/method.h
+++ b/method.h
@@ -73,10 +73,17 @@ typedef struct rb_callable_method_entry_struct { /* same fields with rb_method_e
 #define METHOD_ENTRY_COMPLEMENTED(me)        ((me)->flags & IMEMO_FL_USER3)
 #define METHOD_ENTRY_COMPLEMENTED_SET(me)    ((me)->flags |= IMEMO_FL_USER3)
 #define METHOD_ENTRY_CACHED(me)              ((me)->flags & IMEMO_FL_USER4)
-#define METHOD_ENTRY_CACHED_SET(me)          ((me)->flags |= IMEMO_FL_USER4)
 #define METHOD_ENTRY_INVALIDATED(me)         ((me)->flags & IMEMO_FL_USER5)
 #define METHOD_ENTRY_INVALIDATED_SET(me)     ((me)->flags |= IMEMO_FL_USER5)
 
+static inline void
+METHOD_ENTRY_CACHED_SET(rb_callable_method_entry_t *me)
+{
+    if (!METHOD_ENTRY_CACHED(me)) {
+        me->flags |= IMEMO_FL_USER4;
+    }
+}
+
 static inline void
 METHOD_ENTRY_VISI_SET(rb_method_entry_t *me, rb_method_visibility_t visi)
 {