diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 6e211b67b2736b5f1dcf2328a36d5941d52bf9af..108a1e99aa9fc9911a29c1a5fbfd40a848d21b7d 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -274,7 +274,8 @@ struct cifsSesInfo {
 	int capabilities;
 	char serverName[SERVER_NAME_LEN_WITH_NULL * 2];	/* BB make bigger for
 				TCP names - will ipv6 and sctp addresses fit? */
-	char *user_name;
+	char *user_name;	/* must not be null except during init of sess
+				   and after mount option parsing we fill it */
 	char *domainName;
 	char *password;
 	struct session_key auth_key;
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 68b7dbf24b9281a0c8d922fc1fcad88586f4b147..8d72acbd5c1328a7f8ad0ce9636b996cf35165d5 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -3258,7 +3258,9 @@ cifs_construct_tcon(struct cifs_sb_info *cifs_sb, uid_t fsuid)
 	struct cifsSesInfo *ses;
 	struct cifsTconInfo *tcon = NULL;
 	struct smb_vol *vol_info;
-	char username[MAX_USERNAME_SIZE + 1];
+	char username[28]; /* big enough for "krb50x" + hex of ULONG_MAX 6+16 */
+			   /* We used to have this as MAX_USERNAME which is   */
+			   /* way too big now (256 instead of 32) */
 
 	vol_info = kzalloc(sizeof(*vol_info), GFP_KERNEL);
 	if (vol_info == NULL) {