diff --git a/gc.c b/gc.c
index 58e79e5bc0..8fdf96503a 100644
--- a/gc.c
+++ b/gc.c
@@ -4394,7 +4394,7 @@ is_garbage_object(rb_objspace_t *objspace, VALUE ptr)
     }
 }
 
-static inline int
+static inline bool
 is_live_object(rb_objspace_t *objspace, VALUE ptr)
 {
     switch (BUILTIN_TYPE(ptr)) {