diff --git a/modules/system/system.admin.inc b/modules/system/system.admin.inc
index 3313f5a..75be2e7 100644
--- a/modules/system/system.admin.inc
+++ b/modules/system/system.admin.inc
@@ -628,7 +628,7 @@ function system_theme_settings_validate($form, &$form_state) {
 
   // If the user provided a path for a logo or favicon file, make sure a file
   // exists at that path.
-  if ($form_state['values']['logo_path']) {
+  if (isset($form_state['values']['logo_path']) && $form_state['values']['logo_path']) {
     $path = _system_theme_settings_validate_path($form_state['values']['logo_path']);
     if (!$path) {
       form_set_error('logo_path', t('The custom logo path is invalid.'));