diff --git a/Parser/asdl.py b/Parser/asdl.py
index bd892b6..7620d58 100644
--- a/Parser/asdl.py
+++ b/Parser/asdl.py
@@ -167,7 +167,7 @@
         return Product(fields)
 
     def p_sum_0(self, (constructor,)):
-        " sum ::= constructor """
+        " sum ::= constructor "
         return [constructor]
 
     def p_sum_1(self, (constructor, _, sum)):