diff --git a/runtime/syntax/javascript.vim b/runtime/syntax/javascript.vim
index 8a5e10b..1ab1c2d 100644
--- a/runtime/syntax/javascript.vim
+++ b/runtime/syntax/javascript.vim
@@ -7,7 +7,7 @@
 "		(ss) repaired several quoting and grouping glitches
 "		(ss) fixed regex parsing issue with multiple qualifiers [gi]
 "		(ss) additional factoring of keywords, globals, and members
-" Last Change:	2020 May 14
+" Last Change:	2021 Mar 30
 " 		2013 Jun 12: adjusted javaScriptRegexpString (Kevin Locke)
 " 		2018 Apr 14: adjusted javaScriptRegexpString (LongJohnCoder)
 
@@ -41,6 +41,7 @@
 
 syn match   javaScriptSpecialCharacter "'\\.'"
 syn match   javaScriptNumber	       "-\=\<\d\+L\=\>\|0[xX][0-9a-fA-F]\+\>"
+syn match   javaScriptNumber	       "-\=\<\d\+\%(_\d\+\)*\>"
 syn region  javaScriptRegexpString     start=+[,(=+]\s*/[^/*]+ms=e-1,me=e-1 skip=+\\\\\|\\/+ end=+/[gimuys]\{0,2\}\s*$+ end=+/[gimuys]\{0,2\}\s*[+;.,)\]}]+me=e-1 end=+/[gimuys]\{0,2\}\s\+\/+me=e-1 contains=@htmlPreproc,javaScriptComment oneline
 
 syn keyword javaScriptConditional	if else switch