diff --git a/src/modules/tooltip/Labels.js b/src/modules/tooltip/Labels.js
index 8d87a1e91..303a947b8 100644
--- a/src/modules/tooltip/Labels.js
+++ b/src/modules/tooltip/Labels.js
@@ -237,7 +237,8 @@ export default class Labels {
 
     if (typeof yLbTitleFormatter !== 'function') {
       yLbTitleFormatter = function (label) {
-        return label
+        // refrence used from line: 966 in Options.js
+         return label ? label + ': ' : ''
       }
     }