diff --git a/lib/less/parser.js b/lib/less/parser.js
index afb6fa348..910a01e38 100644
--- a/lib/less/parser.js
+++ b/lib/less/parser.js
@@ -783,7 +783,7 @@ less.Parser = function Parser(env) {
                 // selector for now.
                 //
                 call: function () {
-                    var elements = [], e, c, args = [], arg, index = i, s = input.charAt(i), name, value, important = false;
+                    var elements = [], e, c, argsSemiColon = [], argsComma = [], args, delim, arg, nameLoop, expressions, isSemiColonSeperated, expressionContainsNamed, index = i, s = input.charAt(i), name, value, important = false;
 
                     if (s !== '.' && s !== '#') { return }
                     
@@ -794,31 +794,60 @@ less.Parser = function Parser(env) {
                         c = $('>');
                     }
                     if ($('(')) {
+                        expressions = [];
                         while (arg = $(this.expression)) {
+                            nameLoop = null;
                             value = arg;
-                            name = null;
 
                             // Variable
                             if (arg.value.length == 1) {
                                 var val = arg.value[0];
                                 if (val instanceof tree.Variable) {
                                     if ($(':')) {
-                                        if (value = $(this.expression)) {
-                                            name = val.name;
-                                        } else {
-                                            throw new(Error)("Expected value");
+                                        if (expressions.length > 0) {
+                                            if (isSemiColonSeperated) {
+                                                error("Cannot mix ; and , as delimiter types");
+                                            }
+                                            expressionContainsNamed = true;
                                         }
+                                        value = expect(this.expression);
+                                        nameLoop = (name = val.name);
                                     }
                                 }
                             }
-
-                            args.push({ name: name, value: value });
-
-                            if (! $(',')) { break }
+                            
+                            expressions.push(value);
+                            
+                            argsComma.push({ name: nameLoop, value: value });
+                            
+                            if ($(',')) {
+                                continue;
+                            }
+                            
+                            if ($(';') || isSemiColonSeperated) {
+                            
+                                if (expressionContainsNamed) {
+                                    error("Cannot mix ; and , as delimiter types");
+                                }
+                            
+                                isSemiColonSeperated = true;
+                                                        
+                                if (expressions.length > 1) {
+                                    value = new(tree.Value)(expressions);
+                                }
+                                argsSemiColon.push({ name: name, value: value });
+                            
+                                name = null;
+                                expressions = [];
+                                expressionContainsNamed = false;
+                            }
                         }
-                        if (! $(')')) throw new(Error)("Expected )");
+
+                        expect(')');
                     }
 
+                    args = isSemiColonSeperated ? argsSemiColon : argsComma;
+
                     if ($(this.important)) {
                         important = true;
                     }
@@ -852,7 +881,7 @@ less.Parser = function Parser(env) {
                 definition: function () {
                     var name, params = [], match, ruleset, param, value, cond, variadic = false;
                     if ((input.charAt(i) !== '.' && input.charAt(i) !== '#') ||
-                        peek(/^[^{]*(;|})/)) return;
+                        peek(/^[^{]*\}/)) return;
 
                     save();
 
@@ -862,6 +891,7 @@ less.Parser = function Parser(env) {
                         do {
                             if (input.charAt(i) === '.' && $(/^\.{3}/)) {
                                 variadic = true;
+                                params.push({ variadic: true });
                                 break;
                             } else if (param = $(this.entities.variable) || $(this.entities.literal)
                                                                          || $(this.entities.keyword)) {
@@ -883,7 +913,7 @@ less.Parser = function Parser(env) {
                             } else {
                                 break;
                             }
-                        } while ($(','))
+                        } while ($(',') || $(';'))
 
                         // .mixincall("@{a}"); 
                         // looks a bit like a mixin definition.. so we have to be nice and restore
diff --git a/lib/less/tree/mixin.js b/lib/less/tree/mixin.js
index b441bf3b2..1de625ea7 100644
--- a/lib/less/tree/mixin.js
+++ b/lib/less/tree/mixin.js
@@ -70,42 +70,69 @@ tree.mixin.Definition.prototype = {
     find:      function ()     { return this.parent.find.apply(this, arguments) },
     rulesets:  function ()     { return this.parent.rulesets.apply(this) },
 
-    evalParams: function (env, args) {
-        var frame = new(tree.Ruleset)(null, []), varargs, arg;
+    evalParams: function (env, args, evaldArguments) {
+        var frame = new(tree.Ruleset)(null, []), varargs, arg, params = this.params.slice(0), i, j, val, name, isNamedFound;
+        
+        if (args) {
+            args = args.slice(0);
 
-        for (var i = 0, val, name; i < this.params.length; i++) {
-            arg = args && args[i]
-
-            if (arg && arg.name) {
-                frame.rules.unshift(new(tree.Rule)(arg.name, arg.value.eval(env)));
-                args.splice(i, 1);
-                i--;
-                continue;
+            for(i = 0; i < args.length; i++) {
+                arg = args[i];
+                if (name = (arg && arg.name)) {
+                    isNamedFound = false;
+                    for(j = 0; j < params.length; j++) {
+                        if (!evaldArguments[j] && name === params[j].name) {
+                            evaldArguments[j] = arg.value.eval(env);
+                            frame.rules.unshift(new(tree.Rule)(name, arg.value.eval(env)));
+                            isNamedFound = true;
+                            break;
+                        }
+                    }
+                    if (isNamedFound) {
+                        args.splice(i, 1);
+                        i--;
+                        continue;
+                    } else {
+                        throw { type: 'Runtime', message: "Named argument for " + this.name +
+                            ' ' + args[i].name + ' not found' };
+                    }
+                }
             }
+        }
+
+        for (i = 0; i < params.length; i++) {
+            if (evaldArguments[i]) continue;
+            
+            arg = args && args[i]
 			
-            if (name = this.params[i].name) {
-                if (this.params[i].variadic && args) {
+            if (name = params[i].name) {
+                if (params[i].variadic && args) {
                     varargs = [];
-                    for (var j = i; j < args.length; j++) {
+                    for (j = i; j < args.length; j++) {
                         varargs.push(args[j].value.eval(env));
                     }
                     frame.rules.unshift(new(tree.Rule)(name, new(tree.Expression)(varargs).eval(env)));
-                } else if (val = (arg && arg.value) || this.params[i].value) {
+                } else if (val = (arg && arg.value) || params[i].value) {
                     frame.rules.unshift(new(tree.Rule)(name, val.eval(env)));
+                    evaldArguments[i] = val.eval(env)
                 } else {
                     throw { type: 'Runtime', message: "wrong number of arguments for " + this.name +
                             ' (' + args.length + ' for ' + this.arity + ')' };
                 }
             }
+            
+            if (params[i].variadic && args) {
+                for (j = i; j < args.length; j++) {
+                    evaldArguments[j] = args[j].value.eval(env);
+                }
+            }
         }
+
         return frame;
     },
     eval: function (env, args, important) {
-        var frame = this.evalParams(env, args), context, _arguments = [], rules, start;
+        var _arguments = [], frame = this.evalParams(env, args, _arguments), context, rules, start;
 
-        for (var i = 0; i < Math.max(this.params.length, args && args.length); i++) {
-            _arguments.push((args[i] && args[i].value) || this.params[i].value);
-        }
         frame.rules.unshift(new(tree.Rule)('@arguments', new(tree.Expression)(_arguments).eval(env)));
 
         rules = important ?
@@ -127,13 +154,13 @@ tree.mixin.Definition.prototype = {
         }
 
         if (this.condition && !this.condition.eval({
-            frames: [this.evalParams(env, args)].concat(env.frames)
+            frames: [this.evalParams(env, args, [])].concat(env.frames)
         }))                                                           { return false }
 
         len = Math.min(argsLength, this.arity);
 
         for (var i = 0; i < len; i++) {
-            if (!this.params[i].name) {
+            if (!this.params[i].name && !this.params[i].variadic) {
                 if (args[i].value.eval(env).toCSS() != this.params[i].value.eval(env).toCSS()) {
                     return false;
                 }
diff --git a/test/css/mixins-args.css b/test/css/mixins-args.css
index d5b67f304..365d5fc95 100644
--- a/test/css/mixins-args.css
+++ b/test/css/mixins-args.css
@@ -72,3 +72,20 @@ body {
   border: "{";
   width: "{";
 }
+.comma-vs-semi-colon {
+  one: a;
+  two: b, c;
+  one: d, e;
+  two: f;
+  one: g;
+  one: h;
+  one: i;
+  one: j;
+  one: k;
+  two: l;
+  one: m, n;
+  one: o, p;
+  two: q;
+  one: r, s;
+  two: t;
+}
diff --git a/test/css/mixins-named-args.css b/test/css/mixins-named-args.css
index 1c1afaf8f..e460aa104 100644
--- a/test/css/mixins-named-args.css
+++ b/test/css/mixins-named-args.css
@@ -2,11 +2,18 @@
   color: blue;
   width: 5px;
   height: 99%;
+  args: 1px 100%;
   text-align: center;
 }
 .class {
   width: 5px;
   height: 19%;
+  args: 1px 20%;
+}
+.all-args-wrong-args {
+  width: 10px;
+  height: 9%;
+  args: 2px 10%;
 }
 .named-args2 {
   width: 15px;
diff --git a/test/less/errors/mixed-mixin-definition-args-1.less b/test/less/errors/mixed-mixin-definition-args-1.less
new file mode 100644
index 000000000..9b0e23afa
--- /dev/null
+++ b/test/less/errors/mixed-mixin-definition-args-1.less
@@ -0,0 +1,6 @@
+.mixin(@a : 4, @b : 3, @c: 2) {
+    will: fail;
+}
+.mixin-test {
+    .mixin(@a: 5; @b: 6, @c: 7);
+}
\ No newline at end of file
diff --git a/test/less/errors/mixed-mixin-definition-args-1.txt b/test/less/errors/mixed-mixin-definition-args-1.txt
new file mode 100644
index 000000000..6ceda7d8a
--- /dev/null
+++ b/test/less/errors/mixed-mixin-definition-args-1.txt
@@ -0,0 +1,4 @@
+SyntaxError: Cannot mix ; and , as delimiter types in {path}mixed-mixin-definition-args-1.less:5:29
+4 .mixin-test {
+5     .mixin(@a: 5; @b: 6, @c: 7);
+6 }
diff --git a/test/less/errors/mixed-mixin-definition-args-2.less b/test/less/errors/mixed-mixin-definition-args-2.less
new file mode 100644
index 000000000..c9709427a
--- /dev/null
+++ b/test/less/errors/mixed-mixin-definition-args-2.less
@@ -0,0 +1,6 @@
+.mixin(@a : 4, @b : 3, @c: 2) {
+    will: fail;
+}
+.mixin-test {
+    .mixin(@a: 5, @b: 6; @c: 7);
+}
diff --git a/test/less/errors/mixed-mixin-definition-args-2.txt b/test/less/errors/mixed-mixin-definition-args-2.txt
new file mode 100644
index 000000000..ebb566650
--- /dev/null
+++ b/test/less/errors/mixed-mixin-definition-args-2.txt
@@ -0,0 +1,4 @@
+SyntaxError: Cannot mix ; and , as delimiter types in {path}mixed-mixin-definition-args-2.less:5:25
+4 .mixin-test {
+5     .mixin(@a: 5, @b: 6; @c: 7);
+6 }
diff --git a/test/less/mixins-args.less b/test/less/mixins-args.less
index ea43a0a53..76ba26234 100644
--- a/test/less/mixins-args.less
+++ b/test/less/mixins-args.less
@@ -128,3 +128,27 @@ body {
 .edge-case {
     .mixin-arguments("{");
 }
+
+// semi-colon vs comma for delimiting
+
+.mixin-takes-one(@a) {
+    one: @a;
+}
+
+.mixin-takes-two(@a; @b) {
+    one: @a;
+	two: @b;
+}
+
+.comma-vs-semi-colon {
+    .mixin-takes-two(@a : a; @b : b, c);
+	.mixin-takes-two(@a : d, e; @b : f);
+	.mixin-takes-one(@a: g);
+	.mixin-takes-one(@a : h;);
+	.mixin-takes-one(i);
+	.mixin-takes-one(j;);
+	.mixin-takes-two(k, l);
+	.mixin-takes-one(m, n;);
+	.mixin-takes-two(o, p; q);
+	.mixin-takes-two(r, s; t;);
+}
diff --git a/test/less/mixins-named-args.less b/test/less/mixins-named-args.less
index 57b07d010..afe9ad6b9 100644
--- a/test/less/mixins-named-args.less
+++ b/test/less/mixins-named-args.less
@@ -1,6 +1,7 @@
 .mixin (@a: 1px, @b: 50%) {
   width: @a * 5;
   height: @b - 1%;
+  args: @arguments;
 }
 .mixin (@a: 1px, @b: 50%) when (@b > 75%){
   text-align: center;
@@ -16,6 +17,10 @@
   .mixin(@b: @var);
 }
 
+.all-args-wrong-args {
+  .mixin(@b: 10%, @a: 2px);
+}
+
 .mixin2 (@a: 1px, @b: 50%, @c: 50) {
   width: @a * 5;
   height: @b - 1%;