diff --git a/packages/less/src/less/functions/index.js b/packages/less/src/less/functions/index.js
index 160ac7523..f463c3639 100644
--- a/packages/less/src/less/functions/index.js
+++ b/packages/less/src/less/functions/index.js
@@ -13,6 +13,7 @@ import string from './string';
 import svg from './svg';
 import types from './types';
 import style from './style';
+import size from './size';
 
 export default environment => {
     const functions = { functionRegistry, functionCaller };
@@ -30,6 +31,7 @@ export default environment => {
     functionRegistry.addMultiple(svg(environment));
     functionRegistry.addMultiple(types);
     functionRegistry.addMultiple(style);
+    functionRegistry.addMultiple(size);
 
     return functions;
 };
diff --git a/packages/less/src/less/functions/size.js b/packages/less/src/less/functions/size.js
new file mode 100644
index 000000000..16e61fb4c
--- /dev/null
+++ b/packages/less/src/less/functions/size.js
@@ -0,0 +1,23 @@
+import Variable from '../tree/variable';
+import Anonymous from '../tree/variable';
+
+const sizeExpression = function (args) {
+    args = Array.prototype.slice.call(args);
+    switch (args.length) {
+        case 0: throw { type: 'Argument', message: 'one or more arguments required' };
+    }
+    
+    const entityList = [new Variable(args[0].value, this.index, this.currentFileInfo).eval(this.context)];
+       
+    args = entityList.map(a => { return a.toCSS(this.context); }).join(this.context.compress ? ',' : ', ');
+    
+    return new Anonymous(`size(${args})`);
+};
+
+export default {
+    size: function(...args) {
+        try {
+            return sizeExpression.call(this, args);
+        } catch (e) {}
+    },
+};
diff --git a/packages/less/src/less/parser/parser.js b/packages/less/src/less/parser/parser.js
index 6af533ff3..283d119ae 100644
--- a/packages/less/src/less/parser/parser.js
+++ b/packages/less/src/less/parser/parser.js
@@ -482,13 +482,20 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                     const index = parserInput.i;
 
                     parserInput.save();
-
+                    
+                    let keywordEntity = this.entities.keyword();
+                    parserInput.restore();
+                    parserInput.save();
+                    
                     validCall = parserInput.$re(/^[\w]+\(/);
                     if (!validCall) {
                         parserInput.forget();
                         return;
+                    } else if (validCall && keywordEntity && !functionRegistry.get(validCall.substring(0, validCall.length - 1))) {
+                        parserInput.restore();
+                        return;
                     }
-
+                        
                     validCall = validCall.substring(0, validCall.length - 1);
 
                     let rule = this.ruleProperty();
diff --git a/packages/test-data/css/_main/media.css b/packages/test-data/css/_main/media.css
index 83b241bab..8bd685f87 100644
--- a/packages/test-data/css/_main/media.css
+++ b/packages/test-data/css/_main/media.css
@@ -269,3 +269,11 @@
     padding: 0;
   }
 }
+@media screen and (max-width: 1280px) {
+  .form-process-table {
+    width: 1200px;
+  }
+  .form-process-table > div {
+    width: 960px;
+  }
+}
diff --git a/packages/test-data/less/_main/media.less b/packages/test-data/less/_main/media.less
index 82e9e7cc3..8b9fc0cfd 100644
--- a/packages/test-data/less/_main/media.less
+++ b/packages/test-data/less/_main/media.less
@@ -297,3 +297,12 @@
     }
   }
 }
+
+@media screen and(max-width:1280px) {
+  .form-process-table {
+    width: 1200px;
+    > div {
+      width: 960px;
+    }
+  }
+}