diff --git a/method.h b/method.h
index e2d121d9b8..0cb1b4135a 100644
--- a/method.h
+++ b/method.h
@@ -153,7 +153,7 @@ enum method_optimized_type {
 };
 
 PACKED_STRUCT_UNALIGNED(struct rb_method_definition_struct {
-    unsigned int type :  4; /* method type */
+    BITFIELD(rb_method_type_t) type : 4;
     int alias_count : 28;
     int complemented_count : 28;