diff --git a/src/vs/workbench/browser/parts/activitybar/activitybarPart.ts b/src/vs/workbench/browser/parts/activitybar/activitybarPart.ts
index 75f4d49aa705613f98b158fc5523df1b6129e562..e24e7c1dc4a4d7c450b75dfd0809fe518e42f15a 100644
--- a/src/vs/workbench/browser/parts/activitybar/activitybarPart.ts
+++ b/src/vs/workbench/browser/parts/activitybar/activitybarPart.ts
@@ -293,6 +293,11 @@ export class ActivitybarPart extends Part implements IActivityBarService {
 	}
 
 	private updateViewletSwitcher() {
+		if (!this.viewletSwitcherBar) {
+			// We have not been rendered yet so there is nothing to update.
+			return;
+		}
+
 		let viewletsToShow = this.getPinnedViewlets();
 
 		// Always show the active viewlet even if it is marked to be hidden