diff --git a/src/hammer.h b/src/hammer.h
index 773f3e120a897530fb432e8c99bb8d02b27ce0b6..87252889d53212d357efcd07b10c5812258b7087 100644
--- a/src/hammer.h
+++ b/src/hammer.h
@@ -109,8 +109,8 @@ const parser_t* whitespace(const parser_t* p);
 
 const parser_t* left_factor_action(const parser_t* p);
 
-/* Given a single-character parser, p, returns a single-character parser that will parse any character *other* than the character p would parse. */
-const parser_t* negate(const parser_t* p);
+/* Parse a single character *NOT* in charset */
+const parser_t* notin(const uint8_t charset, int length);
 
 /* A no-argument parser that succeeds if there is no more input to parse. */
 const parser_t* end_p();