diff --git a/src/prepare/webgl/WebGLPrepare.js b/src/prepare/webgl/WebGLPrepare.js
index 0b7a804..0986db5 100644
--- a/src/prepare/webgl/WebGLPrepare.js
+++ b/src/prepare/webgl/WebGLPrepare.js
@@ -44,6 +44,13 @@
      */
     this.completes = [];
 
+    /**
+     * If prepare is ticking (running).
+     * @type {Boolean}
+     * @private
+     */
+    this.ticking = false;
+
     // Add textures and graphics to upload
     this.register(findBaseTextures, uploadBaseTextures)
         .register(findGraphics, uploadGraphics);