diff --git a/lib/less/functions/types.js b/lib/less/functions/types.js
index f6bfae929..7502acf84 100644
--- a/lib/less/functions/types.js
+++ b/lib/less/functions/types.js
@@ -57,6 +57,24 @@ functionRegistry.addMultiple({
     isem: function (n) {
         return isunit(n, 'em');
     },
+    isrem: function (n) {
+        return isunit(n, 'rem');
+    },
+    isvw: function (n) {
+        return isunit(n, 'vw');
+    },
+    isvh: function (n) {
+        return isunit(n, 'vh');
+    },
+    isvmin: function (n) {
+        return isunit(n, 'vmin');
+    },
+    isvmax: function (n) {
+        return isunit(n, 'vmax');
+    },
+    isch: function (n) {
+        return isunit(n, 'ch');
+    },
     isunit: isunit,
     unit: function (val, unit) {
         if (!(val instanceof Dimension)) {
diff --git a/lib/less/tree/unit.js b/lib/less/tree/unit.js
index 0e27daaad..2aa0e8b81 100644
--- a/lib/less/tree/unit.js
+++ b/lib/less/tree/unit.js
@@ -42,7 +42,7 @@ Unit.prototype.is = function (unitString) {
     return this.toString().toUpperCase() === unitString.toUpperCase();
 };
 Unit.prototype.isLength = function () {
-    return Boolean(this.toCSS().match(/px|em|%|in|cm|mm|pc|pt|ex/));
+    return RegExp('^(px|em|rem|in|cm|mm|pc|pt|ex|vw|vh|vmin|vmax)$', 'g').test(this.toCSS());
 };
 Unit.prototype.isEmpty = function () {
     return this.numerator.length === 0 && this.denominator.length === 0;
diff --git a/test/css/functions.css b/test/css/functions.css
index f4144ea2c..8ed26f842 100644
--- a/test/css/functions.css
+++ b/test/css/functions.css
@@ -150,6 +150,12 @@
   pixel: true;
   percent: true;
   em: true;
+  rem: true;
+  vw: true;
+  vh: true;
+  vmin: true;
+  vmax: true;
+  ch: true;
   cat: true;
   no-unit-is-empty: true;
   case-insensitive-1: true;
diff --git a/test/less/functions.less b/test/less/functions.less
index ad8682931..431c26513 100644
--- a/test/less/functions.less
+++ b/test/less/functions.less
@@ -134,11 +134,11 @@
 
   fade-out: fadeout(red, 5%); // support fadeOut and fadeout
   fade-in: fadein(fadeout(red, 10%), 5%);
-  fade-out-relative: fadeout(red, 5%,relative); 
+  fade-out-relative: fadeout(red, 5%,relative);
   fade-in-relative: fadein(fadeout(red, 10%, relative), 5%, relative);
-  fade-out2:  fadeout(fadeout(red, 50%), 50%); 
+  fade-out2:  fadeout(fadeout(red, 50%), 50%);
   fade-out2-relative: fadeout(fadeout(red, 50%, relative), 50%, relative);
-  
+
   hsv: hsv(5, 50%, 30%);
   hsva: hsva(3, 50%, 30%, 0.2);
 
@@ -163,6 +163,12 @@
     pixel: ispixel(32px);
     percent: ispercentage(32%);
     em: isem(32em);
+    rem: isrem(32rem);
+    vw: isvw(32vw);
+    vh: isvh(32vh);
+    vmin: isvmin(32vmin);
+    vmax: isvmax(32vmax);
+    ch: isch(32ch);
     cat: isunit(32cat, cat);
     no-unit-is-empty: isunit(32, '');
     case-insensitive-1: isunit(32CAT, cat);