diff --git a/AsyncDisplayKit/ASNavigationController.m b/AsyncDisplayKit/ASNavigationController.m
index bf97b765f5..e67f15e742 100644
--- a/AsyncDisplayKit/ASNavigationController.m
+++ b/AsyncDisplayKit/ASNavigationController.m
@@ -40,7 +40,10 @@ ASVisibilityDepthImplementation;
 - (NSInteger)visibilityDepthOfChildViewController:(UIViewController *)childViewController
 {
   NSUInteger viewControllerIndex = [self.viewControllers indexOfObject:childViewController];
-  NSAssert(viewControllerIndex != NSNotFound, @"childViewController is not in the navigation stack.");
+  if (viewControllerIndex == NSNotFound) {
+    //If childViewController is not actually a child, return NSNotFound which is also a really large number.
+    return NSNotFound;
+  }
   
   if (viewControllerIndex == self.viewControllers.count - 1) {
     //view controller is at the top, just return our own visibility depth.
diff --git a/AsyncDisplayKit/ASTabBarController.m b/AsyncDisplayKit/ASTabBarController.m
index 65b31d8137..5dd994e084 100644
--- a/AsyncDisplayKit/ASTabBarController.m
+++ b/AsyncDisplayKit/ASTabBarController.m
@@ -39,6 +39,12 @@ ASVisibilityDepthImplementation;
 
 - (NSInteger)visibilityDepthOfChildViewController:(UIViewController *)childViewController
 {
+  NSUInteger viewControllerIndex = [self.viewControllers indexOfObject:childViewController];
+  if (viewControllerIndex == NSNotFound) {
+    //If childViewController is not actually a child, return NSNotFound which is also a really large number.
+    return NSNotFound;
+  }
+  
   if (self.selectedViewController == childViewController) {
     return [self visibilityDepth];
   }