diff --git a/AsyncDisplayKit/Details/ASCollectionViewFlowLayoutInspector.m b/AsyncDisplayKit/Details/ASCollectionViewFlowLayoutInspector.m
index 4d8aa8e287..b1e00770c1 100644
--- a/AsyncDisplayKit/Details/ASCollectionViewFlowLayoutInspector.m
+++ b/AsyncDisplayKit/Details/ASCollectionViewFlowLayoutInspector.m
@@ -63,6 +63,9 @@ static inline ASSizeRange NodeConstrainedSizeForScrollDirection(ASCollectionView
 {
   if (_delegateFlags.implementsConstrainedSizeForNodeAtIndexPath) {
     return [collectionView.asyncDelegate collectionView:collectionView constrainedSizeForNodeAtIndexPath:indexPath];
+  } else {
+    // With 2.0 `collectionView:constrainedSizeForNodeAtIndexPath:` was moved to the delegate. Assert if not implemented on the delegate but on the data source
+    ASDisplayNodeAssert([collectionView.asyncDataSource respondsToSelector:@selector(collectionView:constrainedSizeForNodeAtIndexPath:)] == NO, @"collectionView:constrainedSizeForNodeAtIndexPath: was moved from the ASCollectionDataSource to the ASCollectionDataSource.");
   }
   
   return NodeConstrainedSizeForScrollDirection(collectionView);
@@ -143,6 +146,9 @@ static inline ASSizeRange NodeConstrainedSizeForScrollDirection(ASCollectionView
 {
   if (_delegateFlags.implementsConstrainedSizeForNodeAtIndexPath) {
     return [collectionView.asyncDelegate collectionView:collectionView constrainedSizeForNodeAtIndexPath:indexPath];
+  } else {
+    // With 2.0 `collectionView:constrainedSizeForNodeAtIndexPath:` was moved to the delegate. Assert if not implemented on the delegate but on the data source
+    ASDisplayNodeAssert([collectionView.asyncDataSource respondsToSelector:@selector(collectionView:constrainedSizeForNodeAtIndexPath:)] == NO, @"collectionView:constrainedSizeForNodeAtIndexPath: was moved from the ASCollectionDataSource to the ASCollectionDataSource.");
   }
   
   CGSize itemSize = _layout.itemSize;
diff --git a/AsyncDisplayKitTests/ASCollectionViewFlowLayoutInspectorTests.m b/AsyncDisplayKitTests/ASCollectionViewFlowLayoutInspectorTests.m
index 58de30ff19..027b40fe29 100644
--- a/AsyncDisplayKitTests/ASCollectionViewFlowLayoutInspectorTests.m
+++ b/AsyncDisplayKitTests/ASCollectionViewFlowLayoutInspectorTests.m
@@ -10,6 +10,7 @@
 
 #import <XCTest/XCTest.h>
 #import <UIKit/UIKit.h>
+#import <OCMock/OCMock.h>
 
 #import "ASCollectionView.h"
 #import "ASCollectionViewFlowLayoutInspector.h"
@@ -45,6 +46,27 @@
 
 @end
 
+@protocol InspectorTestDataSourceDelegateProtocol <ASCollectionDataSource, ASCollectionDelegate>
+
+@end
+
+@interface InspectorTestDataSourceDelegateWithoutNodeConstrainedSize : NSObject <InspectorTestDataSourceDelegateProtocol>
+@end
+
+@implementation InspectorTestDataSourceDelegateWithoutNodeConstrainedSize
+
+- (ASCellNodeBlock)collectionView:(ASCollectionView *)collectionView nodeBlockForItemAtIndexPath:(NSIndexPath *)indexPath
+{
+  return ^{ return [[ASCellNode alloc] init]; };
+}
+
+- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
+{
+  return 0;
+}
+
+@end
+
 @interface ASCollectionViewFlowLayoutInspectorTests : XCTestCase
 
 @end
@@ -345,4 +367,50 @@
   collectionView.asyncDelegate = nil;
 }
 
+- (void)testThatItThrowsIfNodeConstrainedSizeIsImplementedOnDataSourceButNotOnDelegateLayoutInspector
+{
+  UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
+  ASCollectionView *collectionView = [[ASCollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:layout];
+  
+  id dataSourceAndDelegate = [OCMockObject mockForProtocol:@protocol(InspectorTestDataSourceDelegateProtocol)];
+  ASSizeRange constrainedSize = ASSizeRangeMake(CGSizeZero, CGSizeZero);
+  NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:0];
+  NSValue *value = [NSValue value:&constrainedSize withObjCType:@encode(ASSizeRange)];
+  [[[dataSourceAndDelegate stub] andReturnValue:value] collectionView:collectionView constrainedSizeForNodeAtIndexPath:indexPath];
+  collectionView.asyncDataSource = dataSourceAndDelegate;
+  
+  id delegate = [InspectorTestDataSourceDelegateWithoutNodeConstrainedSize new];
+  collectionView.asyncDelegate = delegate;
+  
+  ASCollectionViewLayoutInspector *inspector = [[ASCollectionViewLayoutInspector alloc] initWithCollectionView:collectionView];
+  
+  collectionView.layoutInspector = inspector;
+  XCTAssertThrows([inspector collectionView:collectionView constrainedSizeForNodeAtIndexPath:indexPath]);
+  
+  collectionView.asyncDelegate = dataSourceAndDelegate;
+  XCTAssertNoThrow([inspector collectionView:collectionView constrainedSizeForNodeAtIndexPath:indexPath]);
+}
+
+- (void)testThatItThrowsIfNodeConstrainedSizeIsImplementedOnDataSourceButNotOnDelegateFlowLayoutInspector
+{
+  UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
+  ASCollectionView *collectionView = [[ASCollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:layout];
+  
+  id dataSourceAndDelegate = [OCMockObject mockForProtocol:@protocol(InspectorTestDataSourceDelegateProtocol)];
+  ASSizeRange constrainedSize = ASSizeRangeMake(CGSizeZero, CGSizeZero);
+  NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:0];
+  NSValue *value = [NSValue value:&constrainedSize withObjCType:@encode(ASSizeRange)];
+  [[[dataSourceAndDelegate stub] andReturnValue:value] collectionView:collectionView constrainedSizeForNodeAtIndexPath:indexPath];
+  collectionView.asyncDataSource = dataSourceAndDelegate;
+  
+  id delegate = [InspectorTestDataSourceDelegateWithoutNodeConstrainedSize new];
+  collectionView.asyncDelegate = delegate;
+  
+  ASCollectionViewFlowLayoutInspector *inspector = collectionView.layoutInspector;
+  XCTAssertThrows([inspector collectionView:collectionView constrainedSizeForNodeAtIndexPath:indexPath]);
+  
+  collectionView.asyncDelegate = dataSourceAndDelegate;
+  XCTAssertNoThrow([inspector collectionView:collectionView constrainedSizeForNodeAtIndexPath:indexPath]);
+}
+
 @end