diff --git a/includes/datastream.inc b/includes/datastream.inc
index 592870b7..edc0026b 100644
--- a/includes/datastream.inc
+++ b/includes/datastream.inc
@@ -52,7 +52,6 @@ function islandora_view_datastream(AbstractDatastream $datastream, $download = F
   }
   if ($download) {
     // Browsers will not append all extensions.
-    $mime_detect = new MimeDetect();
     $extension = '.' . islandora_get_extension_for_mimetype($datastream->mimetype);
     // Prevent adding on a duplicate extension.
     $label = $datastream->label;
diff --git a/includes/datastream.version.inc b/includes/datastream.version.inc
index 83a94aef..e97640d4 100644
--- a/includes/datastream.version.inc
+++ b/includes/datastream.version.inc
@@ -275,21 +275,23 @@ function islandora_get_object_extensions(AbstractObject $object) {
 function islandora_datastream_version_replace_form($form, &$form_state, AbstractDatastream $datastream) {
   module_load_include('inc', 'islandora', 'includes/content_model');
   module_load_include('inc', 'islandora', 'includes/utilities');
+  module_load_include('inc', 'islandora', 'includes/mimetype.utils');
 
   $object = islandora_object_load($datastream->parent->id);
   $form_state['object_id'] = $object->id;
   $form_state['dsid'] = $datastream->id;
   $form_state['object'] = $object;
   $datastream_mime_map = islandora_get_object_extensions($object);
-  $mime_detect = new MimeDetect();
-  $ext = array();
-  if (isset($datastream_mime_map[$datastream->id])) {
-    foreach ($datastream_mime_map[$datastream->id]['mime'] as $key => $value) {
-      $extensions = $mime_detect->getValidExtensions($value);
-      $ext = array_merge($ext, $extensions);
-    }
+  $current_mime = $datastream->mimetype;
+  $mimes = $datastream_mime_map[$datastream->id]['mime'];
+  if (!in_array($current_mime, $mimes)) {
+    $mimes[] = $current_mime;
+  }
+  $extensions = array();
+  foreach ($mimes as $mime) {
+    $extensions = array_merge($extensions, islandora_get_extensions_for_mimetype($mime));
   }
-  $valid_extensions = implode(' ', $ext);
+  $valid_extensions = implode(' ', $extensions);
   $upload_size = min((int) ini_get('post_max_size'), (int) ini_get('upload_max_filesize'));
   return array(
     'dsid_fieldset' => array(
diff --git a/includes/mimetype.utils.inc b/includes/mimetype.utils.inc
index 989c55cd..1a20859d 100644
--- a/includes/mimetype.utils.inc
+++ b/includes/mimetype.utils.inc
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * @file
  * Mimetype specific utility functions.
@@ -11,17 +12,19 @@
  *   The mimetype whose extension is required.
  *
  * @return string
- *   The extension mapped to the given mimetype.
+ *   The extension mapped to the given mimetype. Defaults to 'bin'.
  */
 function islandora_get_extension_for_mimetype($mimetype) {
   // file.mimetypes.inc is a part of Drupal core, however is not
   // automatically loaded. Manually require it.
   require_once DRUPAL_ROOT . "/includes/file.mimetypes.inc";
-
+  $extension = 'bin';
   $mimetype_mapping = file_mimetype_mapping();
   $extension_index = array_search($mimetype, $mimetype_mapping['mimetypes']);
-  $mime_array_flipped = array_reverse($mimetype_mapping['extensions']);
-  $extension = array_search($extension_index, $mime_array_flipped);
+  if ($extension_index !== FALSE) {
+    $mime_array_flipped = array_reverse($mimetype_mapping['extensions']);
+    $extension = array_search($extension_index, $mime_array_flipped);
+  }
 
   // We can only have one mapping in drupal for 'xml'.
   if ($mimetype == "text/xml") {
@@ -29,3 +32,29 @@ function islandora_get_extension_for_mimetype($mimetype) {
   }
   return $extension;
 }
+
+/**
+ * Retrieve all file extensions for a give mimetype.
+ *
+ * @param string $mimetype
+ *   The mimetype whose extensions are required.
+ *
+ * @return array
+ *   All known legal extensions.
+ */
+function islandora_get_extensions_for_mimetype($mimetype) {
+  // file.mimetypes.inc is a part of Drupal core, however is not
+  // automatically loaded. Manually require it.
+  require_once DRUPAL_ROOT . "/includes/file.mimetypes.inc";
+  $mimetype_mapping = file_mimetype_mapping();
+  $index = array_search($mimetype, $mimetype_mapping['mimetypes']);
+  $extensions = array();
+  if ($index !== FALSE) {
+    $extensions = array_keys($mimetype_mapping['extensions'], $index);
+  }
+  // We can only have one mapping in drupal for 'xml'.
+  if ($mimetype == "text/xml") {
+    $extensions[] = 'xml';
+  }
+  return $extensions;
+}