diff --git a/lib/kref.c b/lib/kref.c
index 1599dbf..a547ad3 100644
--- a/lib/kref.c
+++ b/lib/kref.c
@@ -40,7 +40,7 @@ void kref_init(struct kref *kref)
  */
 void kref_get(struct kref *kref)
 {
-	WARN_ON(!atomic_read(&kref->refcount));
+	WARN_ON(atomic_read(&kref->refcount) <= 0);
 	atomic_inc(&kref->refcount);
 	smp_mb__after_atomic_inc();
 }
@@ -63,7 +63,7 @@ int kref_put(struct kref *kref, void (*release)(struct kref *kref))
 {
 	WARN_ON(release == NULL);
 	WARN_ON(release == (void (*)(struct kref *))kfree);
-	WARN_ON(!atomic_read(&kref->refcount));
+	WARN_ON(atomic_read(&kref->refcount) <= 0);
 
 	if (atomic_dec_and_test(&kref->refcount)) {
 		release(kref);