diff --git a/zen-internals/template.theme-registry.inc b/zen-internals/template.theme-registry.inc
index ac11fd6..07f2f69 100644
--- a/zen-internals/template.theme-registry.inc
+++ b/zen-internals/template.theme-registry.inc
@@ -10,6 +10,12 @@
  * We are simply using this hook as a convenient time to do some related work.
  */
 function _zen_theme(&$existing, $type, $theme, $path) {
+  // When using a Zen subtheme as the installation theme, access permissions
+  // are not yet defined, so we should not continue.
+  if (defined('MAINTENANCE_MODE') && 'install' == MAINTENANCE_MODE) {
+    return array();
+  }
+
   // If we are auto-rebuilding the theme registry, warn about the feature.
   if (
     // Only display for site config admins.