diff --git a/lib/filestorage/file_system_filedir.php b/lib/filestorage/file_system_filedir.php
index 103dcca41e5..192781c30d3 100644
--- a/lib/filestorage/file_system_filedir.php
+++ b/lib/filestorage/file_system_filedir.php
@@ -391,7 +391,14 @@ class file_system_filedir extends file_system {
             ignore_user_abort($prev);
             throw new file_exception('storedfilecannotcreatefile');
         }
-        rename($hashfile.'.tmp', $hashfile);
+        if (!rename($hashfile.'.tmp', $hashfile)) {
+            // Something very strange went wrong.
+            @unlink($hashfile . '.tmp');
+            // Note, we don't try to clean up $hashfile. Almost certainly, if it exists
+            // (e.g. written by another process?) it will be right, so don't wipe it.
+            ignore_user_abort($prev);
+            throw new file_exception('storedfilecannotcreatefile');
+        }
         chmod($hashfile, $this->filepermissions); // Fix permissions if needed.
         @unlink($hashfile.'.tmp'); // Just in case anything fails in a weird way.
         ignore_user_abort($prev);
@@ -465,7 +472,14 @@ class file_system_filedir extends file_system {
             ignore_user_abort($prev);
             throw new file_exception('storedfilecannotcreatefile');
         }
-        rename($hashfile.'.tmp', $hashfile);
+        if (!rename($hashfile.'.tmp', $hashfile)) {
+            // Something very strange went wrong.
+            @unlink($hashfile . '.tmp');
+            // Note, we don't try to clean up $hashfile. Almost certainly, if it exists
+            // (e.g. written by another process?) it will be right, so don't wipe it.
+            ignore_user_abort($prev);
+            throw new file_exception('storedfilecannotcreatefile');
+        }
         chmod($hashfile, $this->filepermissions); // Fix permissions if needed.
         @unlink($hashfile.'.tmp'); // Just in case anything fails in a weird way.
         ignore_user_abort($prev);