diff --git a/devtools/client/shared/widgets/tooltip/EventTooltipHelper.js b/devtools/client/shared/widgets/tooltip/EventTooltipHelper.js
index 8d98dbc05ee7d..01f1b0ec91084 100644
--- a/devtools/client/shared/widgets/tooltip/EventTooltipHelper.js
+++ b/devtools/client/shared/widgets/tooltip/EventTooltipHelper.js
@@ -60,6 +60,7 @@ class EventTooltip extends EventEmitter {
       styleActiveLine: true,
       extraKeys: {},
       theme: "mozilla markup-view",
+      cm6: true,
     };
 
     const doc = this._tooltip.doc;