diff --git a/lib/core.js b/lib/core.js
index e776822..03951e5 100644
--- a/lib/core.js
+++ b/lib/core.js
@@ -396,7 +396,7 @@ var Comb = function(predefinedOptions) {
         var context = options && options.context;
         var tree;
 
-        if (!text) return text;
+        if (!text || !_this.shouldProcessFile(filename)) return text;
 
         // TODO: Parse different syntaxes
         _this.syntax = syntax || 'css';