diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 407ad78..7461597 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -95,9 +95,10 @@ function install_drupal($settings = array()) {
     $output = install_run_tasks($install_state);
   }
   catch (Exception $e) {
-    // When an installation error occurs, either send the error to the web
-    // browser or pass on the exception so the calling script can use it.
-    if ($install_state['interactive']) {
+    // When an installation error occurs, send the error to the web browser
+    // where possible, otherwise pass on the exception so the calling script
+    // can use it.
+    if ($install_state['interactive'] && function_exists('theme')) {
       install_display_output($e->getMessage(), $install_state);
     }
     else {