diff --git a/lib/less/tree/mixin.js b/lib/less/tree/mixin.js
index 94f48efa..078f30e7 100644
--- a/lib/less/tree/mixin.js
+++ b/lib/less/tree/mixin.js
@@ -19,16 +19,45 @@ tree.mixin.Call.prototype = {
         }
     },
     eval: function (env) {
-        var mixins, mixin, args, rules = [], match = false, i, m, f, isRecursive, isOneFound, rule,
-            candidates = [], candidate, conditionResult = [], defaultFunc = tree.defaultFunc,
-            defaultResult, defNone = 0, defTrue = 1, defFalse = 2, count, originalRuleset; 
+      var mixins, mixin, mixinPath, args, rules = [], match = false, i, m, f, isRecursive, isOneFound, rule,
+        candidates = [], candidate, conditionResult = [], defaultFunc = tree.defaultFunc,
+        defaultResult, defFalseEitherCase=-1, defNone = 0, defTrue = 1, defFalse = 2, count, originalRuleset, noArgumentsFilter;
+
+      function calcDefGroup(mixin, mixinPath) {
+          var p, namespace;
+
+          for (f = 0; f < 2; f++) {
+            conditionResult[f] = true;
+            defaultFunc.value(f);
+            for(p = 0; p < mixinPath.length && conditionResult[f]; p++) {
+              namespace = mixinPath[p];
+              if (namespace.matchCondition) {
+                conditionResult[f] = conditionResult[f] && namespace.matchCondition(null, env);
+              }
+            }
+            if (mixin.matchCondition) {
+              conditionResult[f] = conditionResult[f] && mixin.matchCondition(args, env);
+            }
+          }
+          if (conditionResult[0] || conditionResult[1]) {
+            if (conditionResult[0] != conditionResult[1]) {
+              return conditionResult[1] ?
+                defTrue : defFalse;
+            }
+
+            return defNone;
+          }
+          return defFalseEitherCase;
+        }
 
         args = this.arguments && this.arguments.map(function (a) {
             return { name: a.name, value: a.value.eval(env) };
         });
 
+        noArgumentsFilter = function(rule) {return rule.matchArgs(null, env);};
+
         for (i = 0; i < env.frames.length; i++) {
-            if ((mixins = env.frames[i].find(this.selector)).length > 0) {
+            if ((mixins = env.frames[i].find(this.selector, null, noArgumentsFilter)).length > 0) {
                 isOneFound = true;
                 
                 // To make `default()` function independent of definition order we have two "subpasses" here.
@@ -37,7 +66,8 @@ tree.mixin.Call.prototype = {
                 // we make a final decision.
                 
                 for (m = 0; m < mixins.length; m++) {
-                    mixin = mixins[m];
+                    mixin = mixins[m].rule;
+                    mixinPath = mixins[m].path;
                     isRecursive = false;
                     for(f = 0; f < env.frames.length; f++) {
                         if ((!(mixin instanceof tree.mixin.Definition)) && mixin === (env.frames[f].originalRuleset || env.frames[f])) {
@@ -48,28 +78,14 @@ tree.mixin.Call.prototype = {
                     if (isRecursive) {
                         continue;
                     }
-                    
-                    if (mixin.matchArgs(args, env)) {  
-                        candidate = {mixin: mixin, group: defNone};
-                        
-                        if (mixin.matchCondition) { 
-                            for (f = 0; f < 2; f++) {
-                                defaultFunc.value(f);
-                                conditionResult[f] = mixin.matchCondition(args, env);
-                            }
-                            if (conditionResult[0] || conditionResult[1]) {
-                                if (conditionResult[0] != conditionResult[1]) {
-                                    candidate.group = conditionResult[1] ?
-                                        defTrue : defFalse;
-                                }
 
-                                candidates.push(candidate);
-                            }   
+                    if (mixin.matchArgs(args, env)) {
+                        candidate = {mixin: mixin, group: calcDefGroup(mixin, mixinPath)};
+
+                        if (candidate.group!==defFalseEitherCase) {
+                          candidates.push(candidate);
                         }
-                        else {
-                            candidates.push(candidate);
-                        }
-                        
+
                         match = true;
                     }
                 }
@@ -133,6 +149,7 @@ tree.mixin.Call.prototype = {
                     message: this.selector.toCSS().trim() + " is undefined",
                     index:   this.index, filename: this.currentFileInfo.filename };
         }
+
     },
     format: function (args) {
         return this.selector.toCSS().trim() + '(' +
diff --git a/lib/less/tree/ruleset.js b/lib/less/tree/ruleset.js
index 17c0ad1a..f5cdf1f5 100644
--- a/lib/less/tree/ruleset.js
+++ b/lib/less/tree/ruleset.js
@@ -238,9 +238,9 @@ tree.Ruleset.prototype = {
         var rules = this.rules;
         if (rules) { rules.unshift(rule); } else { this.rules = [ rule ]; }
     },
-    find: function (selector, self) {
+    find: function (selector, self, filter) {
         self = self || this;
-        var rules = [], match,
+        var rules = [], match, foundMixins,
             key = selector.toCSS();
 
         if (key in this._lookups) { return this._lookups[key]; }
@@ -251,10 +251,15 @@ tree.Ruleset.prototype = {
                     match = selector.match(rule.selectors[j]);
                     if (match) {
                         if (selector.elements.length > match) {
-                            Array.prototype.push.apply(rules, rule.find(
-                                new(tree.Selector)(selector.elements.slice(match)), self));
+                          if (!filter || filter(rule)) {
+                            foundMixins = rule.find(new(tree.Selector)(selector.elements.slice(match)), self, filter);
+                            for (var i = 0; i < foundMixins.length; ++i) {
+                              foundMixins[i].path.push(rule);
+                            }
+                            Array.prototype.push.apply(rules, foundMixins);
+                          }
                         } else {
-                            rules.push(rule);
+                            rules.push({ rule: rule, path: []});
                         }
                         break;
                     }
diff --git a/test/css/mixins-guards.css b/test/css/mixins-guards.css
index 59b6f932..b918cda6 100644
--- a/test/css/mixins-guards.css
+++ b/test/css/mixins-guards.css
@@ -91,3 +91,11 @@
 .mixin-generated-class {
   a: 1;
 }
+#guarded-caller {
+  guarded: namespace;
+  silent: namespace;
+  guarded: with default;
+}
+#guarded-deeper {
+  should: match 1;
+}
diff --git a/test/less/mixins-guards.less b/test/less/mixins-guards.less
index 5aec2e51..33a35830 100644
--- a/test/less/mixins-guards.less
+++ b/test/less/mixins-guards.less
@@ -171,3 +171,58 @@
 }
 
 #ns > .mixin-for-root-usage(1);
+
+@namespaceGuard: 1;
+#guarded when (@namespaceGuard>0) {
+  #deeper {
+    .mixin() {
+      guarded: namespace;
+    }
+  }
+}
+#guarded() when (@namespaceGuard>0) {
+  #deeper {
+    .mixin() {
+      silent: namespace;
+    }
+  }
+}
+#guarded(@variable) when (@namespaceGuard>0) {
+  #deeper {
+    .mixin() {
+      should: not match because namespace argument;
+    }
+  }
+}
+#guarded(@variable: default) when (@namespaceGuard>0) {
+  #deeper {
+    .mixin() {
+      guarded: with default;
+    }
+  }
+}
+#guarded when (@namespaceGuard<0) {
+  #deeper {
+    .mixin() {
+      should: not match because namespace guard;
+    }
+  }
+}
+#guarded-caller {
+  #guarded > #deeper > .mixin();
+}
+#top {
+  #deeper when (@namespaceGuard<0) {
+    .mixin(@a) {
+      should: not match because namespace guard;
+    }
+  }
+  #deeper() when (@namespaceGuard>0) {
+    .mixin(@a) {
+      should: match @a;
+    }
+  }
+}
+#guarded-deeper {
+  #top > #deeper > .mixin(1);
+}
\ No newline at end of file