--- a/testing/marionette/driver.js
+++ b/testing/marionette/driver.js
@@ -2412,17 +2412,21 @@ GeckoDriver.prototype.takeScreenshot = f
       let highlightEls = [];
 
       for (let h of highlights) {
         let el = this.curBrowser.seenEls.get(h, container);
         highlightEls.push(el);
       }
 
       let canvas = capture.viewport(this.getCurrentWindow(), highlightEls);
-      return capture.toBase64(canvas);
+      if (hash) {
+        return capture.toHash(canvas);
+      } else {
+        return capture.toBase64(canvas);
+      }
 
     case Context.CONTENT:
       if (hash) {
         return this.listener.getScreenshotHash(id, full, highlights);
       } else {
         return this.listener.takeScreenshot(id, full, highlights);
       }
   }