diff --git a/src/Token.php b/src/Token.php
index e83e4fe..c488e2e 100644
--- a/src/Token.php
+++ b/src/Token.php
@@ -34,6 +34,7 @@ class Token extends TokenBase {
           // If this token type extends another token type, then merge in
           // the base token type's tokens.
           if (isset($token_info['tokens'][$base_type])) {
+            $token_info['tokens'] += [$type_key => []];
             $token_info['tokens'][$type_key] += $token_info['tokens'][$base_type];
           }
         }