diff --git a/lib/less/index.js b/lib/less/index.js
index ec37017d..9bf4b7c5 100644
--- a/lib/less/index.js
+++ b/lib/less/index.js
@@ -73,11 +73,12 @@ var less = {
     }
 };
 
-['color',    'directive', 'operation',  'dimension',
- 'keyword',  'variable',  'ruleset',    'element',
- 'selector', 'quoted',    'expression', 'rule',
- 'call',     'url',       'alpha',      'import',
- 'mixin',    'comment',   'anonymous',  'value', 'javascript'
+['color',      'directive', 'operation',  'dimension',
+ 'keyword',    'variable',  'ruleset',    'element',
+ 'selector',   'quoted',    'expression', 'rule',
+ 'call',       'url',       'alpha',      'import',
+ 'mixin',      'comment',   'anonymous',  'value',
+ 'javascript', 'assignment'
 ].forEach(function (n) {
     require('./tree/' + n);
 });
diff --git a/lib/less/parser.js b/lib/less/parser.js
index 29dc210b..f8bee863 100644
--- a/lib/less/parser.js
+++ b/lib/less/parser.js
@@ -502,7 +502,7 @@ less.Parser = function Parser(env) {
                 call: function () {
                     var name, args, index = i;
 
-                    if (! (name = /^([\w-]+|%)\(/.exec(chunks[j]))) return;
+                    if (! (name = /^([\w-]+|%|progid:[\w\.]+)\(/.exec(chunks[j]))) return;
 
                     name = name[1].toLowerCase();
 
@@ -522,7 +522,7 @@ less.Parser = function Parser(env) {
                 arguments: function () {
                     var args = [], arg;
 
-                    while (arg = $(this.expression)) {
+                    while (arg = $(this.entities.assignment) || $(this.expression)) {
                         args.push(arg);
                         if (! $(',')) { break }
                     }
@@ -534,6 +534,19 @@ less.Parser = function Parser(env) {
                            $(this.entities.quoted);
                 },
 
+                // Assignments are argument entities for calls.
+                // They are present in ie filter properties as shown below.
+                //
+                //     filter: progid:DXImageTransform.Microsoft.Alpha( *opacity=50* )
+                //
+
+                assignment: function () {
+                    var key, value;
+                    if ((key = $(/^\w+(?=\s?=)/i)) && $('=') && (value = $(this.entity))) {
+                        return new(tree.Assignment)(key, value);
+                    }
+                },
+
                 //
                 // Parse url() tokens
                 //
diff --git a/lib/less/tree/assignment.js b/lib/less/tree/assignment.js
new file mode 100644
index 00000000..70ce6e2f
--- /dev/null
+++ b/lib/less/tree/assignment.js
@@ -0,0 +1,17 @@
+(function (tree) {
+
+tree.Assignment = function (key, val) {
+    this.key = key;
+    this.value = val;
+};
+tree.Assignment.prototype = {
+    toCSS: function () {
+        return this.key + '=' + (this.value.toCSS ? this.value.toCSS() : this.value);
+    },
+    eval: function (env) {
+        if (this.value.eval) { this.value = this.value.eval(env) }
+        return this;
+    }
+};
+
+})(require('../tree'));
\ No newline at end of file
diff --git a/test/css/ie-filters.css b/test/css/ie-filters.css
new file mode 100644
index 00000000..933318ab
--- /dev/null
+++ b/test/css/ie-filters.css
@@ -0,0 +1,5 @@
+.nav {
+  filter: progid:dximagetransform.microsoft.alpha(opacity=20);
+  filter: progid:dximagetransform.microsoft.alpha(opacity=0);
+  filter: progid:dximagetransform.microsoft.gradient(startColorstr="#333333", endColorstr="#000000", GradientType=0);
+}
diff --git a/test/less/ie-filters.less b/test/less/ie-filters.less
new file mode 100644
index 00000000..bea85b82
--- /dev/null
+++ b/test/less/ie-filters.less
@@ -0,0 +1,8 @@
+@fat: 0;
+@cloudhead: "#000000";
+
+.nav {
+  filter: progid:DXImageTransform.Microsoft.Alpha(opacity = 20);
+  filter: progid:DXImageTransform.Microsoft.Alpha(opacity=@fat);
+  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr="#333333", endColorstr=@cloudhead, GradientType=@fat);
+}
\ No newline at end of file