diff --git a/webapp/src/Service/ExternalContestSourceService.php b/webapp/src/Service/ExternalContestSourceService.php
index c07b747334..6e49f51c2a 100644
--- a/webapp/src/Service/ExternalContestSourceService.php
+++ b/webapp/src/Service/ExternalContestSourceService.php
@@ -536,7 +536,7 @@ protected function loadContest(): void
                 try {
                     // The base URL is the URL of the CCS API root.
                     // Proper is '^(.*\/)contests\/.*/', but PC^2 doesn't expose this (yet).
-                    if (preg_match('/^(.*\/)contest(s\/.*/)?',
+                    if (preg_match('/^(.*\/)contest(s\/.*)/',
                                    $this->source->getSource(), $matches) === 0) {
                         $this->loadingError      = 'Cannot determine base URL. Did you pass a CCS API contest URL?';
                         $this->cachedContestData = null;