diff --git a/src/Quox/Lexer.idr b/src/Quox/Lexer.idr
index 46a1cae..956840d 100644
--- a/src/Quox/Lexer.idr
+++ b/src/Quox/Lexer.idr
@@ -73,7 +73,7 @@ skip lex = match lex $ const Nothing
 simple : List String -> a -> Tokenizer (Maybe a)
 simple str = match (choice $ map exact str) . const . Just
 
-choice : (xs : List (Tokenizer a)) -> {auto 0 _ : So (isCons xs)} -> Tokenizer a
+choice : (xs : List (Tokenizer a)) -> {auto 0 _ : NonEmpty xs} -> Tokenizer a
 choice (t :: ts) = foldl (\a, b => a <|> b) t ts
 
 match : Lexer -> (String -> a) -> Tokenizer (Maybe a)