diff --git a/lib/timeline/optionsTimeline.js b/lib/timeline/optionsTimeline.js
index a6ebbc8d..da4c4803 100644
--- a/lib/timeline/optionsTimeline.js
+++ b/lib/timeline/optionsTimeline.js
@@ -113,7 +113,7 @@ let allOptions = {
   type: {string},
   width: {string, number},
   zoomable: {boolean},
-  zoomKey: {string},
+  zoomKey: {string: ['ctrlKey', 'altKey', 'metaKey', '']},
   zoomMax: {number},
   zoomMin: {number},