diff --git a/lib/less/functions.js b/lib/less/functions.js
index 8c0f1031..699183ce 100644
--- a/lib/less/functions.js
+++ b/lib/less/functions.js
@@ -264,28 +264,34 @@ tree.functions = {
     _minmax: function (isMin, args) {
         args = Array.prototype.slice.call(args);
         switch(args.length) {
-        case 0: throw { type: "Argument", message: "one or more arguments required" };
-        case 1: return args[0];
+            case 0: throw { type: "Argument", message: "one or more arguments required" };
         }
-        var i, j, current, currentUnified, referenceUnified, unit,
+        var i, j, current, currentUnified, referenceUnified, unit, unitStatic, unitClone,
             order  = [], // elems only contains original argument values.
             values = {}; // key is the unit.toString() for unified tree.Dimension values,
                          // value is the index into the order array.
         for (i = 0; i < args.length; i++) {
             current = args[i];
             if (!(current instanceof tree.Dimension)) {
-                order.push(current);
+                if(Array.isArray(args[i].value)) {
+                    Array.prototype.push.apply(args, Array.prototype.slice.call(args[i].value));
+                }
                 continue;
             }
-            currentUnified = current.unify();
-            unit = currentUnified.unit.toString();
-            j = values[unit];
+            currentUnified = current.unit.toString() === "" && unitClone !== undefined ? new(tree.Dimension)(current.value, unitClone).unify() : current.unify();
+            unit = currentUnified.unit.toString() === "" && unitStatic !== undefined ? unitStatic : currentUnified.unit.toString();			
+            unitStatic = unit !== "" && unitStatic === undefined || unit !== "" && order[0].unify().unit.toString() === "" ? unit : unitStatic;
+            unitClone = unit !== "" && unitClone === undefined ? current.unit.toString() : unitClone;
+            j = values[""] !== undefined && unit !== "" && unit === unitStatic ? values[""] : values[unit];
             if (j === undefined) {
+                if(unitStatic !== undefined && unit !== unitStatic) {
+                    throw{ type: "Argument", message: "incompatible types" };
+                }
                 values[unit] = order.length;
                 order.push(current);
                 continue;
             }
-            referenceUnified = order[j].unify();
+            referenceUnified = order[j].unit.toString() === "" && unitClone !== undefined ? new(tree.Dimension)(order[j].value, unitClone).unify() : order[j].unify();
             if ( isMin && currentUnified.value < referenceUnified.value ||
                 !isMin && currentUnified.value > referenceUnified.value) {
                 order[j] = current;
@@ -294,8 +300,7 @@ tree.functions = {
         if (order.length == 1) {
             return order[0];
         }
-        args = order.map(function (a) { return a.toCSS(this.env); })
-                    .join(this.env.compress ? "," : ", ");
+        args = order.map(function (a) { return a.toCSS(this.env); }).join(this.env.compress ? "," : ", ");
         return new(tree.Anonymous)((isMin ? "min" : "max") + "(" + args + ")");
     },
     min: function () {
@@ -304,6 +309,9 @@ tree.functions = {
     max: function () {
         return this._minmax(false, arguments);
     },
+    obtain: function (n) {
+        return new(tree.Anonymous)(n.unit);
+    },
     argb: function (color) {
         return new(tree.Anonymous)(color.toARGB());
     },
diff --git a/lib/less/tree/dimension.js b/lib/less/tree/dimension.js
index 93bed32f..f96078ec 100644
--- a/lib/less/tree/dimension.js
+++ b/lib/less/tree/dimension.js
@@ -161,6 +161,7 @@ tree.UnitConversions = {
         'cm': 0.01,
         'mm': 0.001,
         'in': 0.0254,
+        'px': 0.0254 / 96,
         'pt': 0.0254 / 72,
         'pc': 0.0254 / 72 * 12
     },