diff --git a/fs/namespace.c b/fs/namespace.c
index be601d3..5e1bf61 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1728,7 +1728,7 @@ static bool is_mnt_ns_file(struct dentry *dentry)
 	       dentry->d_fsdata == &mntns_operations;
 }
 
-struct mnt_namespace *to_mnt_ns(struct ns_common *ns)
+static struct mnt_namespace *to_mnt_ns(struct ns_common *ns)
 {
 	return container_of(ns, struct mnt_namespace, ns);
 }