1 files changed, 10 insertions, 4 deletions

diff --git a/src/mailman/rest/helpers.py b/src/mailman/rest/helpers.py
index 8de2632bc..a7bbc2bae 100644
--- a/src/mailman/rest/helpers.py
+++ b/src/mailman/rest/helpers.py
@@ -139,9 +139,12 @@ class CollectionMixin:
         return etag(resource)
 
     def _get_collection(self, request):
-        """Return the collection as a concrete list.
+        """Return the collection as a list-like object.
 
-        This must be implemented by subclasses.
+        The returned value must support iteration and slicing. It can for
+        example be a concrete list or an SQLAlchemy request.
+
+        This method must be implemented by subclasses.
 
         :param request: An http request.
         :return: The collection
@@ -162,9 +165,12 @@ class CollectionMixin:
         # get turned into HTTP 400 errors.
         count = request.get_param_as_int('count', min=0)
         page = request.get_param_as_int('page', min=1)
-        total_size = len(collection)
+        try:
+            total_size = collection.count()
+        except TypeError:
+            total_size = len(collection)
         if count is None and page is None:
-            return 0, total_size, collection
+            return 0, total_size, list(collection)
         list_start = (page - 1) * count
         list_end = page * count
         return list_start, total_size, collection[list_start:list_end]