diff --git a/artiq/compiler/types.py b/artiq/compiler/types.py
index 388b1d6ff..41b3733fa 100644
--- a/artiq/compiler/types.py
+++ b/artiq/compiler/types.py
@@ -191,6 +191,7 @@ class TBuiltin(Type):
 
     def __init__(self, name):
         self.name = name
+        self.attributes = {}
 
     def find(self):
         return self