diff --git a/reactos/ntoskrnl/io/pnpmgr/pnpnotify.c b/reactos/ntoskrnl/io/pnpmgr/pnpnotify.c
index 3c125e52ea7..91ffd138204 100644
--- a/reactos/ntoskrnl/io/pnpmgr/pnpnotify.c
+++ b/reactos/ntoskrnl/io/pnpmgr/pnpnotify.c
@@ -96,6 +96,7 @@ IopNotifyPlugPlayNotification(
 		default:
 		{
 			DPRINT1("IopNotifyPlugPlayNotification(): unknown EventCategory 0x%x UNIMPLEMENTED\n", EventCategory);
+			KeReleaseGuardedMutex(&PnpNotifyListLock);
 			return;
 		}
 	}