diff --git a/modules/core/lib/Stats/Output/File.php b/modules/core/lib/Stats/Output/File.php
index be44d70798c7251e064fc692924966f1f4fa0bc2..00913cdf24f66e5671901d39648f974753e7815e 100644
--- a/modules/core/lib/Stats/Output/File.php
+++ b/modules/core/lib/Stats/Output/File.php
@@ -100,6 +100,7 @@ class File extends \SimpleSAML\Stats\Output
         }
 
         $line = $timestamp.' '.json_encode($data)."\n";
+        /** @psalm-suppress PossiblyNullArgument */
         fwrite($this->file, $line);
     }
 }