diff --git a/src/compiler/GF/Grammar/Lexer.x b/src/compiler/GF/Grammar/Lexer.x
index c579b5609..c236b77fa 100644
--- a/src/compiler/GF/Grammar/Lexer.x
+++ b/src/compiler/GF/Grammar/Lexer.x
@@ -268,7 +268,7 @@ data ParseResult a
 newtype P a = P { unP :: AlexInput -> ParseResult a }
 
 instance Functor P where
-  fmap = (<$>)
+  fmap = liftA
 
 instance Applicative P where
   pure = return