@@ -44,7 +44,7 @@ export class ActionBar extends common.ActionBar {
 
         // Find previous ViewController in the navigation stack
         var indexOfViewController = navController.viewControllers.indexOfObject(viewController);
-        if (indexOfViewController !== NSNotFound && indexOfViewController > 0) {
+        if (indexOfViewController < navController.viewControllers.count && indexOfViewController > 0) {
             previousController = navController.viewControllers[indexOfViewController - 1];
         }
Original file line number	Diff line number	Diff line change
`@@ -44,7 +44,7 @@ export class ActionBar extends common.ActionBar {`
`44`	`44`
`45`	`45`	`// Find previous ViewController in the navigation stack`
`46`	`46`	`var indexOfViewController = navController.viewControllers.indexOfObject(viewController);`
`47`		`- if (indexOfViewController !== NSNotFound && indexOfViewController > 0) {`
	`47`	`+ if (indexOfViewController < navController.viewControllers.count && indexOfViewController > 0) {`
`48`	`48`	`previousController = navController.viewControllers[indexOfViewController - 1];`
`49`	`49`	`}`
`50`	`50`