diff --git a/hsmw-highlight b/hsmw-highlight
index 0de1aca..0494278 100644
--- a/hsmw-highlight
+++ b/hsmw-highlight
@@ -676,7 +676,7 @@ typeset -gA HSMW_HIGHLIGHT_STYLES
   local mybuf="$arg"
   integer idx=start_pos end_idx
 
-  while [[ "$mybuf" = (#b)[^\$\\]#((\$[[:alnum:]_]##(\[[^[:space:]]#\])(#c0,1))|(\$[{](\([a-zA-Z0@%#]##\))(#c0,1)[[:alnum:]_]##(\[[^[:space:]]#\])(#c0,1)[}])|[\\][\'\"\$]|[\\](*))(*) ]]; do
+  while [[ "$mybuf" = (#b)[^\$\\]#((\$[a-zA-Z0-9_]##(\[[^[:space:]]#\])(#c0,1))|(\$[{](\([a-zA-Z0@%#]##\))(#c0,1)[a-zA-Z0-9_]##(\[[^[:space:]]#\])(#c0,1)[}])|[\\][\'\"\$]|[\\](*))(*) ]]; do
     [[ -n "${match[7]}" ]] && {
       idx+=${mbegin[1]}
       mybuf="${match[7]}"