--- a/sites/all/modules/og/og_context/og_context.module 
+++ b/sites/all/modules/og/og_context/og_context.module 
@@ -124,6 +124,13 @@
     'menu path' => array('node/%', 'group/%/%/admin'),
   );
 
+  $providers['file-upload'] = array(
+    'name' => t('File upload'),
+    'description' => t("Determine context by checking the user's session during file uploads."),
+    'callback' => 'og_context_handler_file_upload',
+    'menu path' => array('file/ajax'),
+  );
+
   $providers['user-view'] = array(
     'name' => t('User view'),
     'description' => t("Determine context by checking if a user is a group or a group content on the 'user view' page."),
@@ -332,8 +339,8 @@
  *   The group ID for the current context.
  */
 function og_context_determine_context($group_type, $item = NULL) {
-  // Enable url and node context handlers by default.
-  $defaults = array('url' => -5, 'node' => -4);
+  // Enable url, node, and file-upload context handlers by default.
+  $defaults = array('url' => -5, 'node' => -4, 'file-upload' => -3);
   if (!$enabled_providers = array_keys(variable_get("og_context_negotiation_group_context", $defaults))) {
     return;
   }
@@ -490,6 +497,26 @@
 }
 
 /**
+ * Context handler; For file upload, get context from session.
+ */
+function og_context_handler_file_upload() {
+  $item = menu_get_item();
+  
+  if (strpos($item['path'], 'file/ajax') !== 0) {
+    return;
+  }
+  
+  // For file uploads, use the group in the $_SESSION.
+  // This means that when performing a file upload, there will be a valid
+  // group context when the form is being rebuilt.
+  $gids = array();
+  if (!empty($_SESSION['og_context']['group_type'])) {
+    $gids = array($_SESSION['og_context']['group_type'] => array($_SESSION['og_context']['gid']));
+  }
+  return $gids;
+}
+
+/**
  * Context handler; Get groups from user view.
  */
 function og_context_handler_user_view() {