diff --git a/script/SassScriptFunctions.php b/script/SassScriptFunctions.php
index fc0d4f0..fcbadcf 100755
--- a/script/SassScriptFunctions.php
+++ b/script/SassScriptFunctions.php
@@ -235,6 +235,7 @@ public static function hue($colour)
     return new SassNumber($colour->getHue() . 'deg');
   }
 
+
   /**
    * Returns the saturation component of a colour.
    * @param SassColour $colour The colour
@@ -522,8 +523,16 @@ public static function complement($colour)
    * @see desaturate
    */
   public static function grayscale($colour)
-  {
-    return self::desaturate($colour, new SassNumber(100));
+  { 
+      if(ctype_xdigit($colour))
+      {
+           return self::desaturate($colour, new SassNumber(100));
+      }
+      else
+      {
+          return "";
+      }
+   
   }
 
   /**