diff --git a/data/model/image.py b/data/model/image.py
index d0433708a..bd8fc4302 100644
--- a/data/model/image.py
+++ b/data/model/image.py
@@ -304,6 +304,9 @@ def set_image_metadata(docker_image_id, namespace_name, repository_name, created
 
 
 def set_image_size(docker_image_id, namespace_name, repository_name, image_size, uncompressed_size):
+  if image_size is None:
+    raise DataModelException('Empty image size field')
+
   try:
     image = (Image
              .select(Image, ImageStorage)
@@ -314,7 +317,6 @@ def set_image_size(docker_image_id, namespace_name, repository_name, image_size,
              .where(Repository.name == repository_name, Namespace.username == namespace_name,
                     Image.docker_image_id == docker_image_id)
              .get())
-
   except Image.DoesNotExist:
     raise DataModelException('No image with specified id and repository')
 
@@ -327,15 +329,17 @@ def set_image_size(docker_image_id, namespace_name, repository_name, image_size,
       # TODO(jschorr): Switch to this faster route once we have full ancestor aggregate_size
       # parent_image = Image.get(Image.id == ancestors[-1])
       # total_size = image_size + parent_image.storage.aggregate_size
-      total_size = (ImageStorage
-                    .select(fn.Sum(ImageStorage.image_size))
-                    .join(Image)
-                    .where(Image.id << ancestors)
-                    .scalar()) + image_size
+      ancestor_size = (ImageStorage
+                       .select(fn.Sum(ImageStorage.image_size))
+                       .join(Image)
+                       .where(Image.id << ancestors)
+                       .scalar())
 
       # TODO stop writing to storage when all readers are removed
-      image.storage.aggregate_size = total_size
-      image.aggregate_size = total_size
+      if ancestor_size is not None:
+        total_size = ancestor_size + image_size
+        image.storage.aggregate_size = total_size
+        image.aggregate_size = total_size
     except Image.DoesNotExist:
       pass
   else:
diff --git a/endpoints/v1/registry.py b/endpoints/v1/registry.py
index 5b94c48b5..082a07864 100644
--- a/endpoints/v1/registry.py
+++ b/endpoints/v1/registry.py
@@ -258,15 +258,15 @@ def put_image_layer(namespace, repository, image_id):
       logger.exception('Exception when writing image data')
       abort(520, 'Image %(image_id)s could not be written. Please try again.', image_id=image_id)
 
+  # Save the size of the image.
+  model.image.set_image_size(image_id, namespace, repository, size_info.compressed_size,
+                             size_info.uncompressed_size)
+
   # Append the computed checksum.
   csums = []
   csums.append('sha256:{0}'.format(h.hexdigest()))
 
   try:
-    # Save the size of the image.
-    model.image.set_image_size(image_id, namespace, repository, size_info.compressed_size,
-                               size_info.uncompressed_size)
-
     if requires_tarsum:
       tmp.seek(0)
       csums.append(checksums.compute_tarsum(tmp, json_data))
@@ -331,9 +331,8 @@ def put_image_checksum(namespace, repository, image_id):
   if not repo_image or not repo_image.storage:
     abort(404, 'Image not found: %(image_id)s', issue='unknown-image', image_id=image_id)
 
-  uuid = repo_image.storage.uuid
-
   logger.debug('Looking up repo layer data')
+  uuid = repo_image.storage.uuid
   if not store.exists(repo_image.storage.locations, store.image_json_path(uuid)):
     abort(404, 'Image not found: %(image_id)s', issue='unknown-image', image_id=image_id)
 
@@ -384,7 +383,10 @@ def get_image_json(namespace, repository, image_id, headers):
 
   logger.debug('Looking up repo layer size')
   size = repo_image.storage.image_size
-  headers['X-Docker-Size'] = str(size)
+  if size is not None:
+    # Note: X-Docker-Size is optional and we *can* end up with a NULL image_size,
+    # so handle this case rather than failing.
+    headers['X-Docker-Size'] = str(size)
 
   response = make_response(data, 200)
   response.headers.extend(headers)