diff --git a/src/drawer.js b/src/drawer.js
index 4190bbea..7567e354 100644
--- a/src/drawer.js
+++ b/src/drawer.js
@@ -384,7 +384,7 @@ $.Drawer.prototype = /** @lends OpenSeadragon.Drawer.prototype */{
 
         this.context.save();
         this.context.globalAlpha = opacity;
-        if (compositeOperation !== undefined) {
+        if (compositeOperation !== undefined && compositeOperation !== null) {
             this.context.globalCompositeOperation = compositeOperation;
         }
         this.context.drawImage(