diff --git a/lib/opencv.js b/lib/opencv.js
index 99c951e2..3dbf4f5a 100644
--- a/lib/opencv.js
+++ b/lib/opencv.js
@@ -11,7 +11,7 @@ module.exports = opencv;
 The matrix is one of opencv's most core datatypes.
 
 */
-matrix = opencv.Matrix.prototype;
+var matrix = opencv.Matrix.prototype;
 matrix.__proto__ = EventEmitter.prototype;
 
 matrix.faceDetect = function(classifier, opts, cb){