diff --git a/src/js/parser/javascript/grammar.peg b/src/js/parser/javascript/grammar.peg
index d7fe88b..b05babe 100644
--- a/src/js/parser/javascript/grammar.peg
+++ b/src/js/parser/javascript/grammar.peg
@@ -12,10 +12,7 @@ grammar JavascriptRegexp
   repeat_spec <- ( "{" min:[0-9]+ "," max:[0-9]+ "}"
                  / "{" min:[0-9]+ ",}"
                  / "{" exact:[0-9]+ "}" ) <RepeatSpec>
-  subexp <- "(" capture:( subexp_no_capture / subexp_positive_lookahead / subexp_negative_lookahead )? regexp ")" <Subexp>
-  subexp_no_capture <- "?:"
-  subexp_positive_lookahead <- "?="
-  subexp_negative_lookahead <- "?!"
+  subexp <- "(" capture:( "?:" / "?=" / "?!" )? regexp ")" <Subexp>
   charset <- "[" invert:"^"? parts:( charset_range / charset_terminal )* "]" <Charset>
   charset_range <- first:charset_range_terminal "-" last:charset_range_terminal <CharsetRange>
   charset_terminal <- charset_escape <CharsetEscape>