diff -u b/core/includes/errors.inc b/core/includes/errors.inc
--- b/core/includes/errors.inc
+++ b/core/includes/errors.inc
@@ -153,13 +153,7 @@
  *   TRUE if an error should be displayed.
  */
 function error_displayable($error = NULL) {
-  try {
-    $error_level = config('system.logging')->get('error_level');
-  }
-  catch (Exception $e) {
-    // During very early install the cache_config table does not exist.
-    $error_level = ERROR_REPORTING_DISPLAY_ALL;
-  }
+  $error_level = _drupal_get_error_level();
   $updating = (defined('MAINTENANCE_MODE') && MAINTENANCE_MODE == 'update');
   $all_errors_displayed = ($error_level == ERROR_REPORTING_DISPLAY_ALL) ||
     ($error_level == ERROR_REPORTING_DISPLAY_VERBOSE);
@@ -260,7 +254,7 @@
       $message = format_string('%type: !message in %function (line %line of %file).', $error);
 
       // Check if verbose error reporting is on.
-      $error_level = config('system.logging')->get('error_level');
+      $error_level = _drupal_get_error_level();
 
       if ($error_level == ERROR_REPORTING_DISPLAY_VERBOSE) {
         // First trace is the error itself, already contained in the message.
@@ -293,6 +287,19 @@
 }
 
 /**
+ * Returns the current error level.
+ */
+function _drupal_get_error_level() {
+  try {
+    return config('system.logging')->get('error_level');
+  }
+  catch (Exception $e) {
+    // During very early install the cache_config table does not exist.
+    return ERROR_REPORTING_DISPLAY_ALL;
+  }
+}
+
+/**
  * Gets the last caller from a backtrace.
  *
  * @param $backtrace
only in patch2:
unchanged:
--- a/core/includes/theme.maintenance.inc
+++ b/core/includes/theme.maintenance.inc
@@ -50,7 +50,17 @@ function _drupal_maintenance_theme() {
     //   Stark otherwise. Since there is no low-level access to configuration
     //   currently, we only consult settings.php and fall back to Bartik
     //   otherwise, as it looks generic enough and way more user-friendly.
-    $custom_theme = variable_get('maintenance_theme', config('system.theme')->get('default')) ?: 'bartik';
+    $custom_theme = variable_get('maintenance_theme');
+    if (!$custom_theme)  {
+      $config = config('system.theme');
+      // A broken install might not return an object.
+      if (is_object($config)) {
+        $custom_theme = config('system.theme')->get('default');
+      }
+    }
+    if (!$custom_theme)  {
+      $custom_theme = 'bartik';
+    }
   }
 
   // Ensure that system.module is loaded.