diff --git a/lib/pop3.c b/lib/pop3.c
index 8750374d0d..86e9eca855 100644
--- a/lib/pop3.c
+++ b/lib/pop3.c
@@ -1112,7 +1112,10 @@ static CURLcode pop3_multi_statemach(struct Curl_easy *data, bool *done)
   struct connectdata *conn = data->conn;
   struct pop3_conn *pop3c = &conn->proto.pop3c;
 
-  if(Curl_conn_is_ssl(conn, FIRSTSOCKET) && !pop3c->ssldone) {
+  /* Issue #16166, STLS seems to stall and time out. Revert to previous
+   * check, but it remains to find out why this is wrong. */
+  /* if(Curl_conn_is_ssl(conn, FIRSTSOCKET) && !pop3c->ssldone) { */
+  if((conn->handler->flags & PROTOPT_SSL) && !pop3c->ssldone) {
     bool ssldone = FALSE;
     result = Curl_conn_connect(data, FIRSTSOCKET, FALSE, &ssldone);
     pop3c->ssldone = ssldone;