diff --git a/include/linux/key.h b/include/linux/key.h
index bfc014c..5253471 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -271,7 +271,7 @@
 
 extern struct key *key_lookup(key_serial_t id);
 
-static inline key_serial_t key_serial(struct key *key)
+static inline key_serial_t key_serial(const struct key *key)
 {
 	return key ? key->serial : 0;
 }