diff --git a/lib/less/parser.js b/lib/less/parser.js
index c6c993e6..62321666 100644
--- a/lib/less/parser.js
+++ b/lib/less/parser.js
@@ -785,7 +785,7 @@ less.Parser = function Parser(env) {
                         memo = i;
 
                         if ($(/^when/)) { // Guard
-                            cond = expect(this.condition, 'expected condition');
+                            cond = expect(this.conditions, 'expected condition');
                         }
 
                         ruleset = $(this.block);
@@ -1158,22 +1158,33 @@ less.Parser = function Parser(env) {
                     return operation || m;
                 }
             },
+            conditions: function () {
+                var a, b, index = i, condition;
+
+                if (a = $(this.condition)) {
+                    while ($(',') && (b = $(this.condition))) {
+                        condition = new(tree.Condition)('or', condition || a, b, index);
+                    }
+                    return condition || a;
+                }
+            },
             condition: function () {
-                var a, b, op, index = i, negate = false;
+                var a, b, c, op, index = i, negate = false;
+
                 expect('(');
                 if ($('!')) { negate = true }
                 if (a = $(this.addition) || $(this.entities.keyword) || $(this.entities.quoted)) {
                     if (op = $(/^(?:>=|=<|\!=|[<=>])/)) {
                         if (b = $(this.addition) || $(this.entities.keyword) || $(this.entities.quoted)) {
-                            expect(')');
-                            return new(tree.Condition)(op, a, b, index);
+                            c = new(tree.Condition)(op, a, b, index);
                         } else {
                             error('expected expression');
                         }
                     } else {
-                        expect(')');
-                        return new(tree.Condition)(negate ? '!=' : '=', a, new(tree.Keyword)('true'), index);
+                        c = new(tree.Condition)(negate ? '!=' : '=', a, new(tree.Keyword)('true'), index);
                     }
+                    expect(')');
+                    return $(/^and/) ? new(tree.Condition)('and', c, $(this.condition)) : c;
                 }
             },
 
diff --git a/lib/less/tree/condition.js b/lib/less/tree/condition.js
index e6737a85..9dcdbf70 100644
--- a/lib/less/tree/condition.js
+++ b/lib/less/tree/condition.js
@@ -11,20 +11,27 @@ tree.Condition.prototype.eval = function (env) {
         b = this.rvalue.eval(env);
 
     var i = this.index, result
-    
-    if (a.compare) {
-        result = a.compare(b);
-    } else if (b.compare) {
-        result = b.compare(a);
-    } else {
-        throw { type: "Type",
-                message: "Unable to perform comparison",
-                index: i };
-    }
-    switch (result) {
-        case -1: return this.op === '<' || this.op === '=<' || this.op === '!=';
-        case  0: return this.op === '=' || this.op === '>=' || this.op === '=<';
-        case  1: return this.op === '>' || this.op === '>=' || this.op === '!=';
+
+    switch (this.op) {
+        case 'and':
+            return a && b;
+        case 'or':
+            return a || b;
+        default:
+            if (a.compare) {
+                result = a.compare(b);
+            } else if (b.compare) {
+                result = b.compare(a);
+            } else {
+                throw { type: "Type",
+                        message: "Unable to perform comparison",
+                        index: i };
+            }
+            switch (result) {
+                case -1: return this.op === '<' || this.op === '=<' || this.op === '!=';
+                case  0: return this.op === '=' || this.op === '>=' || this.op === '=<';
+                case  1: return this.op === '>' || this.op === '>=' || this.op === '!=';
+            }
     }
 };
 
diff --git a/test/css/mixins-guards.css b/test/css/mixins-guards.css
index 034ed67c..d7e92db3 100644
--- a/test/css/mixins-guards.css
+++ b/test/css/mixins-guards.css
@@ -45,3 +45,12 @@
 .test5 {
   content: "false.";
 }
+.bool1 {
+  content: true and true;
+  content: true;
+  content: false, true;
+  content: false and true and true, true;
+  content: false, true and true;
+  content: false, false, true;
+  content: false, true and true and true, false;
+}
diff --git a/test/less/mixins-guards.less b/test/less/mixins-guards.less
index c6b5a316..c131c287 100644
--- a/test/less/mixins-guards.less
+++ b/test/less/mixins-guards.less
@@ -72,3 +72,19 @@
 .test3 { .test(1) }
 .test4 { .test(boo) }
 .test5 { .test("true") }
+
+// Boolean expressions
+
+.bool () when (true) and (false)                             { content: true and false } // FALSE
+.bool () when (true) and (true)                              { content: true and true } // TRUE
+.bool () when (true)                                         { content: true } // TRUE
+.bool () when (false) and (false)                            { content: true } // FALSE
+.bool () when (false), (true)                                { content: false, true } // TRUE
+.bool () when (false) and (true) and (true),  (true)         { content: false and true and true, true } // TRUE
+.bool () when (true)  and (true) and (false), (false)        { content: true and true and false, false } // FALSE
+.bool () when (false), (true) and (true)                     { content: false, true and true } // TRUE
+.bool () when (false), (false), (true)                       { content: false, false, true } // TRUE
+.bool () when (false), (false) and (true), (false)           { content: false, false and true, false } // FALSE
+.bool () when (false), (true) and (true) and (true), (false) { content: false, true and true and true, false } // TRUE
+
+.bool1 { .bool }