diff --git a/lib/ext/glx.js b/lib/ext/glx.js
index 63d3c05..eace56b 100644
--- a/lib/ext/glx.js
+++ b/lib/ext/glx.js
@@ -164,7 +164,7 @@ exports.requireExt = function(display, callback)
                 function(buf, opt) {
                     var format = Buffer(count);
                     format.fill('L');
-                    return buf.unpack(format.toString());
+                    return buf.unpack('xxxxxxxxxxxxxxxxxxxxxxxx' + format.toString());
                 },
                 callback
             ];