diff --git a/Source/Internal/IGListAdapter+UICollectionView.m b/Source/Internal/IGListAdapter+UICollectionView.m
index 84d0973f..c6b97d37 100644
--- a/Source/Internal/IGListAdapter+UICollectionView.m
+++ b/Source/Internal/IGListAdapter+UICollectionView.m
@@ -176,7 +176,12 @@
 
 - (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
     IGAssert(![self.collectionViewDelegate respondsToSelector:_cmd], @"IGListAdapter is consuming method also implemented by the collectionViewDelegate: %@", NSStringFromSelector(_cmd));
-    return [self sizeForItemAtIndexPath:indexPath];
+    
+    CGSize size = [self sizeForItemAtIndexPath:indexPath];
+    IGAssert(!isnan(size.height), @"IGListAdapter returned NaN height = %f for item at indexPath <%@>", size.height, indexPath);
+    IGAssert(!isnan(size.width), @"IGListAdapter returned NaN width = %f for item at indexPath <%@>", size.width, indexPath);
+    
+    return size;
 }
 
 - (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
diff --git a/Tests/IGListAdapterTests.m b/Tests/IGListAdapterTests.m
index f80655d1..7ef91479 100644
--- a/Tests/IGListAdapterTests.m
+++ b/Tests/IGListAdapterTests.m
@@ -18,6 +18,7 @@
 #import "IGListAdapterInternal.h"
 #import "IGListTestAdapterDataSource.h"
 #import "IGListTestAdapterHorizontalDataSource.h"
+#import "IGListTestOffsettingLayout.h"
 #import "IGListTestSection.h"
 #import "IGTestSupplementarySource.h"
 #import "IGTestNibSupplementaryView.h"
@@ -1327,6 +1328,42 @@
     XCTAssertEqual(size.height, 0.0);
 }
 
+- (void)test_whenSectionControllerReturnsNANHeight_thatAssertionFires {
+    self.adapter.collectionView.collectionViewLayout = [IGListTestOffsettingLayout new];
+    self.dataSource.objects = @[@1];
+    [self.adapter reloadDataWithCompletion:nil];
+    
+    IGListTestSection *section = [self.adapter sectionControllerForObject:self.dataSource.objects[0]];
+    section.size = CGSizeMake(NAN, 1);
+    
+    NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:0];
+    XCTAssertThrows([self.adapter collectionView:self.collectionView layout:self.collectionView.collectionViewLayout sizeForItemAtIndexPath:indexPath]);
+}
+
+- (void)test_whenSectionControllerReturnsNANWidth_thatAssertionFires {
+    self.adapter.collectionView.collectionViewLayout = [IGListTestOffsettingLayout new];
+    self.dataSource.objects = @[@1];
+    [self.adapter reloadDataWithCompletion:nil];
+    
+    IGListTestSection *section = [self.adapter sectionControllerForObject:self.dataSource.objects[0]];
+    section.size = CGSizeMake(1, NAN);
+    
+    NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:0];
+    XCTAssertThrows([self.adapter collectionView:self.collectionView layout:self.collectionView.collectionViewLayout sizeForItemAtIndexPath:indexPath]);
+}
+
+- (void)test_whenSectionControllerReturnsNANWidthNANHeight_thatAssertionFires {
+    self.adapter.collectionView.collectionViewLayout = [IGListTestOffsettingLayout new];
+    self.dataSource.objects = @[@1];
+    [self.adapter reloadDataWithCompletion:nil];
+    
+    IGListTestSection *section = [self.adapter sectionControllerForObject:self.dataSource.objects[0]];
+    section.size = CGSizeMake(NAN, NAN);
+    
+    NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:0];
+    XCTAssertThrows([self.adapter collectionView:self.collectionView layout:self.collectionView.collectionViewLayout sizeForItemAtIndexPath:indexPath]);
+}
+
 - (void)test_whenSupplementarySourceReturnsNegativeSize_thatAdapterReturnsZero {
     self.dataSource.objects = @[@1];
     [self.adapter reloadDataWithCompletion:nil];