diff --git a/lib/less/functions.js b/lib/less/functions.js
index 1fb7301a..ef9fa685 100644
--- a/lib/less/functions.js
+++ b/lib/less/functions.js
@@ -217,22 +217,22 @@ tree.functions = {
     unit: function (val, unit) {
         return new(tree.Dimension)(val.value, unit ? unit.toCSS() : "");
     },
+    convert: function (val, unit) {
+        return val.convertTo(unit.value);
+    },
     round: function (n, f) {
         var fraction = typeof(f) === "undefined" ? 0 : f.value;
-        return this._math(function(num) { return num.toFixed(fraction); }, n);
+        return this._math(function(num) { return num.toFixed(fraction); }, null, n);
     },
-    ceil: function (n) {
-        return this._math(Math.ceil, n);
+    pi: function () {
+        return new(tree.Dimension)(Math.PI);
     },
-    floor: function (n) {
-        return this._math(Math.floor, n);
+    mod: function(a, b) {
+        return new(tree.Dimension)(a.value % b.value, a.unit);
     },
-    sqrt: function (n) {
-        return this._math(Math.sqrt, n);
-    },
-    _math: function (fn, n) {
+    _math: function (fn, unit, n) {
         if (n instanceof tree.Dimension) {
-            return new(tree.Dimension)(fn(parseFloat(n.value)), n.unit);
+            return new(tree.Dimension)(fn(parseFloat(n.value)), unit == null ? n.unit : unit);
         } else if (typeof(n) === 'number') {
             return fn(n);
         } else {
@@ -383,6 +383,22 @@ tree.functions = {
     }
 };
 
+var mathFunctions = [{name:"ceil"}, {name:"floor"}, {name: "sqrt"}, {name:"abs"},
+        {name:"tan", unit: ""}, {name:"sin", unit: ""}, {name:"cos", unit: ""},
+        {name:"atan", unit: "rad"}, {name:"asin", unit: "rad"}, {name:"acos", unit: "rad"}],
+    createMathFunction = function(name, unit) {
+        return function(n) {
+            if (unit != null) {
+                n = n.unify();
+            }
+            return this._math(Math[name], unit, n);
+        };
+    };
+
+for(var i = 0; i < mathFunctions.length; i++) {
+    tree.functions[mathFunctions[i].name] = createMathFunction(mathFunctions[i].name, mathFunctions[i].unit);
+}
+
 function hsla(color) {
     return tree.functions.hsla(color.h, color.s, color.l, color.a);
 }
diff --git a/lib/less/tree/dimension.js b/lib/less/tree/dimension.js
index f9daa1f6..949433b9 100644
--- a/lib/less/tree/dimension.js
+++ b/lib/less/tree/dimension.js
@@ -20,7 +20,7 @@ tree.Dimension.prototype = {
 
         if (env && env.compress) {
             // Zero values doesn't need a unit
-            if (value === 0) {
+            if (value === 0 && !this.unit.isAngle()) {
                 return strValue;
             }
 
@@ -89,12 +89,22 @@ tree.Dimension.prototype = {
     },
 
     unify: function () {
-      return this.convertTo({ length: 'm', duration: 's' });
+      return this.convertTo({ length: 'm', duration: 's', angle: 'rad' });
     },
 
     convertTo: function (conversions) {
       var value = this.value, unit = this.unit.clone(),
-          i, groupName, group, conversion, targetUnit;
+          i, groupName, group, conversion, targetUnit, derivedConversions = {};
+
+      if (typeof conversions === 'string') {
+          for(i in tree.UnitConversions) {
+              if (tree.UnitConversions[i].hasOwnProperty(conversions)) {
+                  derivedConversions = {};
+                  derivedConversions[i] = conversions;
+              }
+          }
+          conversions = derivedConversions;
+      }
 
       for (groupName in conversions) {
         if (conversions.hasOwnProperty(groupName)) {
@@ -134,8 +144,14 @@ tree.UnitConversions = {
     'pc': 0.0254 / 72 * 12
   },
   duration: {
-     's': 1,
+    's': 1,
     'ms': 0.001
+  },
+  angle: {
+    'rad': 1/(2*Math.PI),
+    'deg': 1/360,
+    'grad': 1/400,
+    'turn': 1
   }
 };
 
@@ -165,6 +181,10 @@ tree.Unit.prototype = {
     return this.toCSS() === unitString;
   },
 
+  isAngle: function () {
+    return tree.UnitConversions.angle.hasOwnProperty(this.toCSS());
+  },
+
   isEmpty: function () {
     return this.numerator.length == 0 && this.denominator.length == 0;
   },
diff --git a/test/css/compression/compression.css b/test/css/compression/compression.css
index 13fe4de5..ddf95b52 100644
--- a/test/css/compression/compression.css
+++ b/test/css/compression/compression.css
@@ -1,2 +1,2 @@
 #colours{color1:#fea;color2:#fea;color3:rgba(255,238,170,0.1);string:"#ffeeaa"}
-dimensions{val:.1px;val:0;val:4cm;val:.2;val:5}
+dimensions{val:.1px;val:0;val:4cm;val:.2;val:5;angles-must-have-unit:0deg}
diff --git a/test/css/functions.css b/test/css/functions.css
index c480a231..d4d3b6e4 100644
--- a/test/css/functions.css
+++ b/test/css/functions.css
@@ -59,6 +59,15 @@
   ceil: 11px;
   floor: 12px;
   sqrt: 5px;
+  pi: 3.141592653589793;
+  mod: 2m;
+  abs: 4%;
+  tan: 0.8390996311772799;
+  sin: 0.17364817766693033;
+  cos: 0.8438539587324921;
+  atan: 0.1rad;
+  atan: 34.00000000000001deg;
+  atan: 45.00000000000001deg;
   percentage: 20%;
   color: #ff0011;
   tint: #898989;
diff --git a/test/less/compression/compression.less b/test/less/compression/compression.less
index bc7b63a7..758a212e 100644
--- a/test/less/compression/compression.less
+++ b/test/less/compression/compression.less
@@ -11,4 +11,5 @@ dimensions {
   val: 4cm;
   val: 0.2;
   val: 5;
+  angles-must-have-unit: 0deg;
 }
\ No newline at end of file
diff --git a/test/less/functions.less b/test/less/functions.less
index 780ef2cb..d8388dee 100644
--- a/test/less/functions.less
+++ b/test/less/functions.less
@@ -65,6 +65,15 @@
   ceil: ceil(10.1px);
   floor: floor(12.9px);
   sqrt: sqrt(25px);
+  pi: pi();
+  mod: mod(13m, 11cm); // could take into account units, doesn't at the moment
+  abs: abs(-4%);
+  tan: tan(40deg);
+  sin: sin(10deg);
+  cos: cos(12);
+  atan: atan(tan(0.1rad));
+  atan: convert(acos(cos(34deg)), deg);
+  atan: convert(acos(cos(50grad)), deg);
   percentage: percentage(10px / 50);
   color: color("#ff0011");
   tint: tint(#777777, 13);