diff --git a/app/models/concerns/sort_handler.rb b/app/models/concerns/sort_handler.rb
index 065fa7fea..519eccc8b 100644
--- a/app/models/concerns/sort_handler.rb
+++ b/app/models/concerns/sort_handler.rb
@@ -19,7 +19,7 @@ module SortHandler
     end
 
     def sort_on_waiting_since(sort_direction = :asc)
-      order(generate_sql_query("waiting_since #{sort_direction.to_s.upcase} NULLS LAST, created_at ASC"))
+      order(generate_sql_query("(waiting_since IS NULL), waiting_since #{sort_direction.to_s.upcase}, created_at ASC"))
     end
 
     def last_messaged_conversations
diff --git a/spec/models/conversation_spec.rb b/spec/models/conversation_spec.rb
index 89c090207..0bf90859e 100644
--- a/spec/models/conversation_spec.rb
+++ b/spec/models/conversation_spec.rb
@@ -879,6 +879,31 @@ RSpec.describe Conversation do
           conversation_4.id
         ]
       end
+
+      context 'when some conversations have a null waiting_since' do
+        before do
+          # rubocop:disable Rails/SkipsModelValidations
+          conversation_5.update_column(:waiting_since, nil)
+          conversation_2.update_column(:waiting_since, nil)
+          # rubocop:enable Rails/SkipsModelValidations
+        end
+
+        it 'places null waiting_since conversations at the end in ascending order' do
+          records = described_class.sort_on_waiting_since
+          expect(records.map(&:id)).to eq [
+            conversation_4.id, conversation_6.id, conversation_7.id, conversation_3.id, conversation_1.id,
+            conversation_5.id, conversation_2.id
+          ]
+        end
+
+        it 'places null waiting_since conversations at the end in descending order' do
+          records = described_class.sort_on_waiting_since(:desc)
+          expect(records.map(&:id)).to eq [
+            conversation_1.id, conversation_3.id, conversation_7.id, conversation_6.id, conversation_4.id,
+            conversation_5.id, conversation_2.id
+          ]
+        end
+      end
     end
   end