diff --git a/lib/filestorage/file_storage.php b/lib/filestorage/file_storage.php
index 0fb99228193..b5d6fdd72fb 100644
--- a/lib/filestorage/file_storage.php
+++ b/lib/filestorage/file_storage.php
@@ -2004,9 +2004,9 @@ class file_storage {
             ignore_user_abort($prev);
             throw new file_exception('storedfilecannotcreatefile');
         }
-        if (filesize($hashfile.'.tmp') !== $filesize) {
-            // This should not happen.
-            unlink($hashfile.'.tmp');
+        if (sha1_file($hashfile.'.tmp') !== $contenthash) {
+            // Highly unlikely edge case, but this can happen on an NFS volume with no space remaining.
+            @unlink($hashfile.'.tmp');
             ignore_user_abort($prev);
             throw new file_exception('storedfilecannotcreatefile');
         }