diff --git a/doc/rust.md b/doc/rust.md
index 975e4bbb8a209..10fb203d022d6 100644
--- a/doc/rust.md
+++ b/doc/rust.md
@@ -297,7 +297,7 @@ the following forms:
 num_lit : nonzero_dec [ dec_digit | '_' ] * num_suffix ?
         | '0' [       [ dec_digit | '_' ] + num_suffix ?
               | 'b'   [ '1' | '0' | '_' ] + int_suffix ?
-              | 'x'   [ hex_digit | '-' ] + int_suffix ? ] ;
+              | 'x'   [ hex_digit | '_' ] + int_suffix ? ] ;
 
 num_suffix : int_suffix | float_suffix ;