diff --git a/AsyncDisplayKit/ASPagerNode.m b/AsyncDisplayKit/ASPagerNode.m
index e7a93b11a1..21310e754e 100644
--- a/AsyncDisplayKit/ASPagerNode.m
+++ b/AsyncDisplayKit/ASPagerNode.m
@@ -14,6 +14,8 @@
 #import "ASDelegateProxy.h"
 #import "ASDisplayNode+Subclasses.h"
 #import "ASPagerFlowLayout.h"
+#import "ASAssert.h"
+#import "ASCellNode.h"
 
 @interface ASPagerNode () <ASCollectionDataSource, ASCollectionDelegate, ASCollectionViewDelegateFlowLayout, ASDelegateProxyInterceptor>
 {
@@ -21,11 +23,16 @@
 
   __weak id <ASPagerDataSource> _pagerDataSource;
   ASPagerNodeProxy *_proxyDataSource;
-  BOOL _pagerDataSourceImplementsNodeBlockAtIndex;
+  struct {
+    unsigned nodeBlockAtIndex:1;
+    unsigned nodeAtIndex:1;
+  } _pagerDataSourceFlags;
 
   __weak id <ASPagerDelegate> _pagerDelegate;
+  struct {
+    unsigned constrainedSizeForNode:1;
+  } _pagerDelegateFlags;
   ASPagerNodeProxy *_proxyDelegate;
-  BOOL _pagerDelegateImplementsConstrainedSizeForNode;
 }
 
 @end
@@ -122,12 +129,17 @@
 
 - (ASCellNodeBlock)collectionNode:(ASCollectionNode *)collectionNode nodeBlockForItemAtIndexPath:(NSIndexPath *)indexPath
 {
-  ASDisplayNodeAssert(_pagerDataSource != nil, @"ASPagerNode must have a data source to load nodes to display");
-  if (!_pagerDataSourceImplementsNodeBlockAtIndex) {
+  if (_pagerDataSourceFlags.nodeBlockAtIndex) {
+    return [_pagerDataSource pagerNode:self nodeBlockAtIndex:indexPath.item];
+  } else if (_pagerDataSourceFlags.nodeAtIndex) {
     ASCellNode *node = [_pagerDataSource pagerNode:self nodeAtIndex:indexPath.item];
     return ^{ return node; };
+  } else {
+    ASDisplayNodeFailAssert(@"Pager data source must implement either %@ or %@. Data source: %@", NSStringFromSelector(@selector(pagerNode:nodeBlockAtIndex:)), NSStringFromSelector(@selector(pagerNode:nodeAtIndex:)), _pagerDataSource);
+    return ^{
+      return [[ASCellNode alloc] init];
+    };
   }
-  return [_pagerDataSource pagerNode:self nodeBlockAtIndex:indexPath.item];
 }
 
 - (NSInteger)collectionNode:(ASCollectionNode *)collectionNode numberOfItemsInSection:(NSInteger)section
@@ -140,7 +152,7 @@
 
 - (ASSizeRange)collectionNode:(ASCollectionNode *)collectionNode constrainedSizeForItemAtIndexPath:(NSIndexPath *)indexPath
 {
-  if (_pagerDelegateImplementsConstrainedSizeForNode) {
+  if (_pagerDelegateFlags.constrainedSizeForNode) {
     return [_pagerDelegate pagerNode:self constrainedSizeForNodeAtIndex:indexPath.item];
   }
 
@@ -159,9 +171,12 @@
   if (dataSource != _pagerDataSource) {
     _pagerDataSource = dataSource;
     
-    _pagerDataSourceImplementsNodeBlockAtIndex = [_pagerDataSource respondsToSelector:@selector(pagerNode:nodeBlockAtIndex:)];
-    // Data source must implement pagerNode:nodeBlockAtIndex: or pagerNode:nodeAtIndex:
-    ASDisplayNodeAssertTrue(_pagerDataSourceImplementsNodeBlockAtIndex || [_pagerDataSource respondsToSelector:@selector(pagerNode:nodeAtIndex:)]);
+    if (dataSource == nil) {
+      memset(&_pagerDataSourceFlags, 0, sizeof(_pagerDataSourceFlags));
+    } else {
+      _pagerDataSourceFlags.nodeBlockAtIndex = [_pagerDataSource respondsToSelector:@selector(pagerNode:nodeBlockAtIndex:)];
+      _pagerDataSourceFlags.nodeAtIndex = [_pagerDataSource respondsToSelector:@selector(pagerNode:nodeAtIndex:)];
+    }
     
     _proxyDataSource = dataSource ? [[ASPagerNodeProxy alloc] initWithTarget:dataSource interceptor:self] : nil;
     
@@ -174,7 +189,11 @@
   if (delegate != _pagerDelegate) {
     _pagerDelegate = delegate;
     
-    _pagerDelegateImplementsConstrainedSizeForNode = [_pagerDelegate respondsToSelector:@selector(pagerNode:constrainedSizeForNodeAtIndex:)];
+    if (delegate == nil) {
+      memset(&_pagerDelegateFlags, 0, sizeof(_pagerDelegateFlags));
+    } else {
+    	_pagerDelegateFlags.constrainedSizeForNode = [_pagerDelegate respondsToSelector:@selector(pagerNode:constrainedSizeForNodeAtIndex:)];
+    }
     
     _proxyDelegate = delegate ? [[ASPagerNodeProxy alloc] initWithTarget:delegate interceptor:self] : nil;
     
diff --git a/AsyncDisplayKitTests/ASViewControllerTests.m b/AsyncDisplayKitTests/ASViewControllerTests.m
index e7c7038ceb..24a24a3fce 100644
--- a/AsyncDisplayKitTests/ASViewControllerTests.m
+++ b/AsyncDisplayKitTests/ASViewControllerTests.m
@@ -34,7 +34,7 @@
   XCTAssertNotEqual(scrollNode.view.contentInset.top, 0);
 }
 
-- (void)DISABLED_testThatViewControllerFrameIsRightAfterCustomTransitionWithNonextendedEdges
+- (void)testThatViewControllerFrameIsRightAfterCustomTransitionWithNonextendedEdges
 {
   UIWindow *window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
   ASDisplayNode *node = [[ASDisplayNode alloc] init];