diff --git a/switchtheme.module b/switchtheme.module
index b52d87a..7702093 100644
--- a/switchtheme.module
+++ b/switchtheme.module
@@ -116,7 +116,7 @@ function switchtheme_custom_theme($return_single = TRUE) {
     $custom_theme['get'] = $_GET['theme'];
   }
   // Check whether the user session contains a custom theme.
-  if (isset($_SESSION['custom_theme'])) {
+  if (empty($user->theme) && isset($_SESSION['custom_theme'])) {
     $custom_theme['session'] = $_SESSION['custom_theme'];
   }
   // Check whether the current user has a custom theme assigned.