diff -u b/core/lib/Drupal/Core/Theme/ThemeManager.php b/core/lib/Drupal/Core/Theme/ThemeManager.php
--- b/core/lib/Drupal/Core/Theme/ThemeManager.php
+++ b/core/lib/Drupal/Core/Theme/ThemeManager.php
@@ -398,7 +398,7 @@
 
     // Add base hook and the hook that is being called to suggestions.
     $suggestions[] = $hook;
-    if ($info['base hook']) {
+    if (isset($info['base hook'])) {
       $suggestions[] = $info['base hook'];
     }
 
@@ -419,7 +419,7 @@
 
     if ($theme->getEngine()) {
         $prefixes[] = $theme->getEngine() . '_engine';
-        $prefixes[] = $base->getName();
+        $prefixes[] = $theme->getName();
     }
 
     foreach (array_reverse($theme->getBaseThemes()) as $base) {