diff --git a/fs/open.c b/fs/open.c
index 54198538b67e..a4b12022edaa 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -903,6 +903,18 @@ struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags)
 	int error;
 	struct file *f;
 
+	/*
+	 * We must always pass in a valid mount pointer.   Historically
+	 * callers got away with not passing it, but we must enforce this at
+	 * the earliest possible point now to avoid strange problems deep in the
+	 * filesystem stack.
+	 */
+	if (!mnt) {
+		printk(KERN_WARNING "%s called with NULL vfsmount\n", __func__);
+		dump_stack();
+		return ERR_PTR(-EINVAL);
+	}
+
 	error = -ENFILE;
 	f = get_empty_filp();
 	if (f == NULL) {