diff --git a/lib/less/parser.js b/lib/less/parser.js
index d732e1b1..3aa54882 100644
--- a/lib/less/parser.js
+++ b/lib/less/parser.js
@@ -542,7 +542,7 @@ less.Parser = function Parser(env) {
                 keyword: function () {
                     var k;
 
-                    if (k = $(/^[_A-Za-z-][_A-Za-z0-9-]*/)) { 
+                    if (k = $(/^[_A-Za-z-][_A-Za-z0-9-]*/)) {
                         if (tree.colors.hasOwnProperty(k)) {
                             // detect named color
                             return new(tree.Color)(tree.colors[k].slice(1));
@@ -995,7 +995,7 @@ less.Parser = function Parser(env) {
 
                 if (! $('[')) return;
 
-                if (key = $(/^[a-zA-Z-]+/) || $(this.entities.quoted)) {
+                if (key = $(/^[a-zA-Z0-9_-]+/) || $(this.entities.quoted)) {
                     if ((op = $(/^[|~*$^]?=/)) &&
                         (val = $(this.entities.quoted) || $(/^[\w-]+/))) {
                         attr = [key, op, val.toCSS ? val.toCSS() : val].join('');
@@ -1117,7 +1117,7 @@ less.Parser = function Parser(env) {
 
             mediaFeatures: function () {
                 var e, features = [];
-                
+
                 do {
                   if (e = $(this.mediaFeature)) {
                       features.push(e);
@@ -1127,7 +1127,7 @@ less.Parser = function Parser(env) {
                       if (! $(',')) { break }
                   }
                 } while (e);
-                
+
                 return features.length > 0 ? features : null;
             },
 
diff --git a/test/css/css-3.css b/test/css/css-3.css
index 45bdc40d..a4497d40 100644
--- a/test/css/css-3.css
+++ b/test/css/css-3.css
@@ -10,6 +10,9 @@
 .other {
   -moz-transform: translate(0, 11em) rotate(-90deg);
 }
+.item[data-cra_zy-attr1b-ut3=bold] {
+  font-weight: bold;
+}
 p:not([class*="lead"]) {
   color: black;
 }
diff --git a/test/less/css-3.less b/test/less/css-3.less
index bdda76d0..e8e4c836 100644
--- a/test/less/css-3.less
+++ b/test/less/css-3.less
@@ -1,4 +1,4 @@
-.comma-delimited { 
+.comma-delimited {
   background: url(bg.jpg) no-repeat, url(bg.png) repeat-x top left, url(bg);
   text-shadow: -1px -1px 1px red, 6px 5px 5px yellow;
   -moz-box-shadow: 0pt 0pt 2px rgba(255, 255, 255, 0.4) inset,
@@ -12,8 +12,11 @@
 .other {
   -moz-transform: translate(0, 11em) rotate(-90deg);
 }
+.item[data-cra_zy-attr1b-ut3=bold] {
+  font-weight: bold;
+}
 p:not([class*="lead"]) {
-  color: black; 
+  color: black;
 }
 
 input[type="text"].class#id[attr=32]:not(1) {
@@ -24,7 +27,7 @@ div#id.class[a=1][b=2].class:not(1) {
   color: white;
 }
 
-ul.comma > li:not(:only-child)::after { 
+ul.comma > li:not(:only-child)::after {
   color: white;
 }