diff --git a/webapp/src/Service/SubmissionService.php b/webapp/src/Service/SubmissionService.php
index 7bca8c9460..1c5c664a7a 100644
--- a/webapp/src/Service/SubmissionService.php
+++ b/webapp/src/Service/SubmissionService.php
@@ -34,7 +34,7 @@
 
 class SubmissionService
 {
-    final public const FILENAME_REGEX = '/^[a-zA-Z0-9][a-zA-Z0-9+_\.-]*$/';
+    final public const FILENAME_REGEX = '/^[a-zA-Z0-9_][a-zA-Z0-9+_\.-]*$/';
     final public const PROBLEM_RESULT_MATCHSTRING = ['@EXPECTED_RESULTS@: ', '@EXPECTED_SCORE@: '];
     final public const PROBLEM_RESULT_REMAP = [
         'ACCEPTED' => 'CORRECT',