diff --git a/core/includes/file.inc b/core/includes/file.inc
index ed4bdce..78fc08e 100644
--- a/core/includes/file.inc
+++ b/core/includes/file.inc
@@ -931,8 +931,35 @@ function file_unmanaged_copy($source, $destination = NULL, $replace = FILE_EXIST
   }
   // Make sure the .htaccess files are present.
   file_ensure_htaccess();
+
+  // Perform the replace operation. Since there could be multiple processes
+  // writing to the same file, the best option is to create a temporary file in
+  // the same directory and then rename it to the destination. A temporary file
+  // is needed if the directory is mounted on a separate machine; thus ensuring
+  // the rename command stays local.
+  $result = FALSE;
+  if ($replace == FILE_EXISTS_REPLACE) {
+    // Get a temporary filename in the destination directory.
+    $temporary_file = drupal_tempnam(drupal_dirname($destination), 'file');
+    // Place contents in the temporary file.
+    if ($temporary_file && @copy($source, $temporary_file)) {
+      if (!$result = @rename($temporary_file, $destination)) {
+        // Unlink and try again for windows. Rename on windows does not replace
+        // the file if it already exists.
+        @unlink($destination);
+        $result = @rename($temporary_file, $destination);
+      }
+      // Remove temporary_file if rename failed.
+      if (!$result) {
+        @unlink($temporary_file);
+      }
+    }
+  }
   // Perform the copy operation.
-  if (!@copy($source, $destination)) {
+  else {
+    $result = @copy($source, $destination);
+  }
+  if ($result === FALSE) {
     // If the copy failed and realpaths exist, retry the operation using them
     // instead.
     if ($real_source === FALSE || $real_destination === FALSE || !@copy($real_source, $real_destination)) {