diff --git a/packages/less/src/less/functions/math-helper.js b/packages/less/src/less/functions/math-helper.js
index b557875c5..4cca18668 100644
--- a/packages/less/src/less/functions/math-helper.js
+++ b/packages/less/src/less/functions/math-helper.js
@@ -1,6 +1,15 @@
+import Call from '../tree/call';
+import CustomProperty from '../tree/custom-property';
 import Dimension from '../tree/dimension';
 
 const MathHelper = (fn, unit, n) => {
+    if (n instanceof Call && n.name === 'var') {
+        if (n.args && n.args.length === 1) {
+            return new Call(fn.name, [new CustomProperty(n.args[0].toCSS(), n._index, n._fileInfo)], n._index, n._fileInfo);
+        } else {
+            throw { type: 'Argument', message: 'var must contain one expression' };
+        }
+    }
     if (!(n instanceof Dimension)) {
         throw { type: 'Argument', message: 'argument must be a number' };
     }
diff --git a/packages/less/src/less/parser/parser.js b/packages/less/src/less/parser/parser.js
index 59aa2eef4..8b2ad6e42 100644
--- a/packages/less/src/less/parser/parser.js
+++ b/packages/less/src/less/parser/parser.js
@@ -794,6 +794,18 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                 if (parserInput.currentChar() === '@' && (name = parserInput.$re(/^(@[\w-]+)\s*:/))) { return name[1]; }
             },
 
+            //
+            // The custom property part of a variable definition.
+            //
+            //     --fink:
+            //
+            customProperty: function () {
+                var name;
+                if (parserInput.currentChar() === '-' && (name = parserInput.$re(/^(--[\w-]+)\s*:/))) {
+                    return name[1];
+                }
+            },
+
             //
             // Call a variable value to retrieve a detached ruleset
             // or a value from a detached ruleset's rules.
@@ -1558,7 +1570,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
 
                 parserInput.save();
 
-                name = this.variable() || this.ruleProperty();
+                name = this.variable() || this.customProperty() || this.ruleProperty();
                 if (name) {
                     isVariable = typeof name === 'string';
 
@@ -1577,7 +1589,7 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                         merge = !isVariable && name.length > 1 && name.pop().value;
 
                         // Custom property values get permissive parsing
-                        if (name[0].value && name[0].value.slice(0, 2) === '--') {
+                        if (isVariable && name.startsWith('--')) {
                             value = this.permissiveValue(/[;}]/);
                         }
                         // Try to store values as anonymous
diff --git a/packages/less/src/less/tree/custom-property.js b/packages/less/src/less/tree/custom-property.js
new file mode 100644
index 000000000..3eaa284b9
--- /dev/null
+++ b/packages/less/src/less/tree/custom-property.js
@@ -0,0 +1,18 @@
+/* eslint-disable no-prototype-builtins */
+import Node from './node';
+
+const CustomProperty = function (name, index, currentFileInfo) {
+    this.name = name;
+    this._index = index;
+    this._fileInfo = currentFileInfo;
+};
+
+CustomProperty.prototype = Object.assign(new Node(), {
+    type: 'CustomProperty',
+
+    genCSS: function (context, output) {
+        output.add('var(' + this.name + ')');
+    }
+});
+
+export default CustomProperty;
diff --git a/packages/less/src/less/tree/operation.js b/packages/less/src/less/tree/operation.js
index 2805326be..982d571d5 100644
--- a/packages/less/src/less/tree/operation.js
+++ b/packages/less/src/less/tree/operation.js
@@ -2,6 +2,7 @@ import Node from './node';
 import Color from './color';
 import Dimension from './dimension';
 import * as Constants from '../constants';
+import Call from './call';
 const MATH = Constants.Math;
 
 
@@ -19,7 +20,15 @@ Operation.prototype = Object.assign(new Node(), {
     },
 
     eval(context) {
-        let a = this.operands[0].eval(context), b = this.operands[1].eval(context), op;
+        var a = this.evalVariable(context, this.operands[0])
+        if (!a) {
+            a = this.operands[0].eval(context)
+        }
+        var b = this.evalVariable(context, this.operands[1]);
+        if (!b) {
+            b = this.operands[1].eval(context);
+        }
+        var op;
 
         if (context.isMathOn(this.op)) {
             op = this.op === './' ? '/' : this.op;
@@ -56,7 +65,41 @@ Operation.prototype = Object.assign(new Node(), {
             output.add(' ');
         }
         this.operands[1].genCSS(context, output);
-    }
+    },
+
+    find: function (obj, fun) {
+        for (var i_2 = 0, r = void 0; i_2 < obj.length; i_2++) {
+            r = fun.call(obj, obj[i_2]);
+            if (r) {
+                return r;
+            }
+        }
+        return null;
+    },
+
+    evalVariable: function (context, operand) {
+        if (operand.name === 'var' && operand.args.length === 1) {
+            var varName = operand.args[0].toCSS();
+            var variable = this.find(context.frames, function (frame) {
+                var v = frame.variable(varName);
+                if (v) {
+                    if (v.important) {
+                        var importantScope = context.importantScope[context.importantScope.length - 1];
+                        importantScope.important = v.important;
+                    }
+                    // If in calc, wrap vars in a function call to cascade evaluate args first
+                    if (context.inCalc) {
+                        return (new Call('_SELF', [v.value])).eval(context);
+                    }
+                    else {
+                        return v.value.eval(context);
+                    }
+                }
+            });
+            
+            return variable;
+        }
+    },
 });
 
 export default Operation;
diff --git a/packages/less/src/less/tree/ruleset.js b/packages/less/src/less/tree/ruleset.js
index a3324cf07..878ac3f80 100644
--- a/packages/less/src/less/tree/ruleset.js
+++ b/packages/less/src/less/tree/ruleset.js
@@ -286,7 +286,7 @@ Ruleset.prototype = Object.assign(new Node(), {
     variables() {
         if (!this._variables) {
             this._variables = !this.rules ? {} : this.rules.reduce(function (hash, r) {
-                if (r instanceof Declaration && r.variable === true) {
+                if (r instanceof Declaration && (r.variable === true  || (typeof r.name ==='string' && r.name.startsWith('--')))) {
                     hash[r.name] = r;
                 }
                 // when evaluating variables in an import statement, imports have not been eval'd
diff --git a/packages/test-data/css/_main/custom-property.css b/packages/test-data/css/_main/custom-property.css
new file mode 100644
index 000000000..243947443
--- /dev/null
+++ b/packages/test-data/css/_main/custom-property.css
@@ -0,0 +1,16 @@
+.test {
+  --basic-deg: 20deg;
+  --basic-deg-tan: tan(var(--basic-deg));
+}
+.test2 {
+  --some-var: 5%;
+  prop: min(95%, 10px);
+}
+.test3 {
+  --some-var: 55%;
+  prop: min(60%, 15px);
+}
+.test4 {
+  color: red;
+  --other-color: green;
+}
diff --git a/packages/test-data/less/_main/custom-property.less b/packages/test-data/less/_main/custom-property.less
new file mode 100644
index 000000000..960267dcd
--- /dev/null
+++ b/packages/test-data/less/_main/custom-property.less
@@ -0,0 +1,19 @@
+.test {
+    --basic-deg: 20deg;
+    --basic-deg-tan: tan(var(--basic-deg));
+}
+
+.test2 {
+    --some-var: 5%;
+    prop: min(100% - var(--some-var), 10px);
+}
+
+.test3 {
+    --some-var: 55%;
+    prop: min(var(--some-var) + 5%, 15px);
+}
+
+.test4 {
+    color: red;
+    --other-color: green;
+}