diff --git a/tambo_en.html b/tambo_en.html
index d62b1cce..d794ecd0 100644
--- a/tambo_en.html
+++ b/tambo_en.html
@@ -101,6 +101,7 @@
 
   if ( brand === 'phet-io' ) {
     preloads = preloads.concat( [
+      '../chipper/js/phet-io/phetioCompareAPIs.js',
       '../phet-io/js/phet-io-initialize-globals.js',
       '../tambo/js/tambo-phet-io-overrides.js'
     ] );