diff --git a/lib/less/parser/parser.js b/lib/less/parser/parser.js
index 145f442f3..f63d6ba56 100644
--- a/lib/less/parser/parser.js
+++ b/lib/less/parser/parser.js
@@ -54,14 +54,16 @@ var Parser = function Parser(context, imports, fileInfo) {
         );
     }
 
-    function expect(arg, msg, index) {
+    function expect(arg, msg) {
         // some older browsers return typeof 'function' for RegExp
         var result = (arg instanceof Function) ? arg.call(parsers) : parserInput.$re(arg);
         if (result) {
             return result;
         }
-        error(msg || (typeof arg === 'string' ? 'expected \'' + arg + '\' got \'' + parserInput.currentChar() + '\''
-                                               : 'unexpected token'));
+        
+        error(msg || (typeof arg === 'string'
+            ? 'expected \'' + arg + '\' got \'' + parserInput.currentChar() + '\''
+            : 'unexpected token'));
     }
 
     // Specialization of expect()
@@ -1963,13 +1965,13 @@ var Parser = function Parser(context, imports, fileInfo) {
             conditions: function () {
                 var a, b, index = parserInput.i, condition;
 
-                a = this.condition();
+                a = this.condition(true);
                 if (a) {
                     while (true) {
                         if (!parserInput.peek(/^,\s*(not\s*)?\(/) || !parserInput.$char(',')) {
                             break;
                         }
-                        b = this.condition();
+                        b = this.condition(true);
                         if (!b) {
                             break;
                         }
@@ -1978,19 +1980,19 @@ var Parser = function Parser(context, imports, fileInfo) {
                     return condition || a;
                 }
             },
-            condition: function () {
+            condition: function (needsParens) {
                 var result, logical, next;
                 function or() {
                     return parserInput.$str('or');
                 }
 
-                result = this.conditionAnd(this);
+                result = this.conditionAnd(needsParens);
                 if (!result) {
                     return ;
                 }
                 logical = or();
                 if (logical) {
-                    next = this.condition();
+                    next = this.condition(needsParens);
                     if (next) {
                         result = new(tree.Condition)(logical, result, next);
                     } else {
@@ -1999,22 +2001,26 @@ var Parser = function Parser(context, imports, fileInfo) {
                 }
                 return result;
             },
-            conditionAnd: function () {
-                var result, logical, next;
-                function insideCondition(me) {
-                    return me.negatedCondition() || me.parenthesisCondition();
+            conditionAnd: function (needsParens) {
+                var result, logical, next, self = this;
+                function insideCondition() {
+                    var cond = self.negatedCondition(needsParens) || self.parenthesisCondition(needsParens);
+                    if (!cond && !needsParens) {
+                        return self.atomicCondition(needsParens);
+                    }
+                    return cond;
                 }
                 function and() {
                     return parserInput.$str('and');
                 }
 
-                result = insideCondition(this);
+                result = insideCondition();
                 if (!result) {
                     return ;
                 }
                 logical = and();
                 if (logical) {
-                    next = this.conditionAnd();
+                    next = this.conditionAnd(needsParens);
                     if (next) {
                         result = new(tree.Condition)(logical, result, next);
                     } else {
@@ -2023,20 +2029,20 @@ var Parser = function Parser(context, imports, fileInfo) {
                 }
                 return result;
             },
-            negatedCondition: function () {
+            negatedCondition: function (needsParens) {
                 if (parserInput.$str('not')) {
-                    var result = this.parenthesisCondition();
+                    var result = this.parenthesisCondition(needsParens);
                     if (result) {
                         result.negate = !result.negate;
                     }
                     return result;
                 }
             },
-            parenthesisCondition: function () {
+            parenthesisCondition: function (needsParens) {
                 function tryConditionFollowedByParenthesis(me) {
                     var body;
                     parserInput.save();
-                    body = me.condition();
+                    body = me.condition(needsParens);
                     if (!body) {
                         parserInput.restore();
                         return ;
@@ -2061,7 +2067,7 @@ var Parser = function Parser(context, imports, fileInfo) {
                     return body;
                 }
 
-                body = this.atomicCondition();
+                body = this.atomicCondition(needsParens);
                 if (!body) {
                     parserInput.restore();
                     return ;
@@ -2073,7 +2079,7 @@ var Parser = function Parser(context, imports, fileInfo) {
                 parserInput.forget();
                 return body;
             },
-            atomicCondition: function () {
+            atomicCondition: function (needsParens) {
                 var entities = this.entities, index = parserInput.i, a, b, c, op;
 
                 function cond() {
diff --git a/test/css/functions.css b/test/css/functions.css
index 6f52648d7..35803f56a 100644
--- a/test/css/functions.css
+++ b/test/css/functions.css
@@ -222,5 +222,10 @@ html {
   c: 3;
   e: ;
   f: 6;
+  g: 3;
+  h: 5;
+  i: 6;
+  j: 8;
+  k: 1;
   /* results in void */
 }
diff --git a/test/less/errors/mixins-guards-cond-expected.less b/test/less/errors/mixins-guards-cond-expected.less
new file mode 100644
index 000000000..e645e416f
--- /dev/null
+++ b/test/less/errors/mixins-guards-cond-expected.less
@@ -0,0 +1,5 @@
+.max (@a, @b) when @a {
+  width: @b;
+}
+
+.max1 { .max(3, 6) }
\ No newline at end of file
diff --git a/test/less/errors/mixins-guards-cond-expected.txt b/test/less/errors/mixins-guards-cond-expected.txt
new file mode 100644
index 000000000..15161ad65
--- /dev/null
+++ b/test/less/errors/mixins-guards-cond-expected.txt
@@ -0,0 +1,3 @@
+SyntaxError: expected condition in {path}mixins-guards-cond-expected.less on line 1, column 20:
+1 .max (@a, @b) when @a {
+2   width: @b;
diff --git a/test/less/functions.less b/test/less/functions.less
index d2744f33a..0228bf0cb 100644
--- a/test/less/functions.less
+++ b/test/less/functions.less
@@ -246,7 +246,7 @@ html {
 #boolean {
   a: boolean(not(2 < 1));
   b: boolean(not(2 > 1) and (true));
-  c: boolean(not(boolean((true))));
+  c: boolean(not(boolean(true)));
 }
 
 #if {
@@ -255,8 +255,13 @@ html {
   @1: if(not(false), {c: 3}, {d: 4}); @1();
 
   e: if(not(true), 5);
-  @f: boolean((3 = 4));
+  @f: boolean(3 = 4);
   f: if(not(@f), 6);
+  g: if(true, 3, 5);
+  h: if(false, 3, 5);
+  i: if(true and isnumber(6), 6, 8);
+  j: if(not(true) and true, 6, 8);
+  k: if(true or true, 1);
 
-  if((false), {g: 7}); /* results in void */
+  if(false, {g: 7}); /* results in void */
 }