diff --git a/lib/vauth/cleartext.c b/lib/vauth/cleartext.c
index a10edbdc74..be6d6111e2 100644
--- a/lib/vauth/cleartext.c
+++ b/lib/vauth/cleartext.c
@@ -74,7 +74,7 @@ CURLcode Curl_auth_create_plain_message(struct Curl_easy *data,
   plen = strlen(passwdp);
 
   /* Compute binary message length. Check for overflows. */
-  if((ulen > SIZE_T_MAX/2) || (plen > (SIZE_T_MAX/2 - 2)))
+  if((ulen > SIZE_T_MAX/4) || (plen > (SIZE_T_MAX/2 - 2)))
     return CURLE_OUT_OF_MEMORY;
   plainlen = 2 * ulen + plen + 2;