diff --git a/lib/less/parser.js b/lib/less/parser.js
index 24b9212f..6ae052c1 100644
--- a/lib/less/parser.js
+++ b/lib/less/parser.js
@@ -832,6 +832,7 @@ less.Parser = function Parser(env) {
                         expressions = [];
                         while (arg = $(this.expression)) {
                             nameLoop = null;
+                            arg.throwAwayComments();
                             value = arg;
 
                             // Variable
@@ -1470,7 +1471,8 @@ less.Parser = function Parser(env) {
 
                 while (e = $(this.addition) || $(this.entity)) {
                     entities.push(e);
-                    if (!peek(/^\/\*/) && (delim = $('/'))) {
+                    // operations do not allow keyword "/" dimension (e.g. small/20px) so we support that here
+                    if (!peek(/^\/[\/*]/) && (delim = $('/'))) {
                         entities.push(new(tree.Anonymous)(delim));
                     }
                 }
diff --git a/lib/less/tree/expression.js b/lib/less/tree/expression.js
index 762db055..e6e970f4 100644
--- a/lib/less/tree/expression.js
+++ b/lib/less/tree/expression.js
@@ -29,6 +29,11 @@ tree.Expression.prototype = {
         return this.value.map(function (e) {
             return e.toCSS ? e.toCSS(env) : '';
         }).join(' ');
+    },
+    throwAwayComments: function () {
+        this.value = this.value.filter(function(v) {
+            return !(v instanceof tree.Comment);
+        });
     }
 };
 
diff --git a/test/less/comments.less b/test/less/comments.less
index 85007c44..4aa2b8f1 100644
--- a/test/less/comments.less
+++ b/test/less/comments.less
@@ -58,7 +58,7 @@
 .selector /* .with */, .lots, /* of */ .comments {
   color: grey, /* blue */ orange;
   -webkit-border-radius: 2px /* webkit only */;
-  -moz-border-radius: 2px * 4 /* moz only with operation */;
+  -moz-border-radius: (2px * 4) /* moz only with operation */;
 }
 
 .mixin_def_with_colors(@a: white, // in