diff --git a/app/helpers/messages/attachment_presentation.rb b/app/helpers/messages/attachment_presentation.rb
index 82ce92d..eec9a3b 100644
--- a/app/helpers/messages/attachment_presentation.rb
+++ b/app/helpers/messages/attachment_presentation.rb
@@ -40,9 +40,10 @@ class Messages::AttachmentPresentation
       end
     end
 
+    # A preview is processed once the frame is drawn, but the poster is a variant of that frame, which can fail on its own.
     def video_poster_url
       poster = message.attachment.preview(:poster)
-      url_for(poster) if poster.processed?
+      url_for(poster) if poster.processed? && poster.image.variant(poster.variation).processed?
     end
 
     def lightboxed_image_preview_tag
diff --git a/test/helpers/messages_helper_test.rb b/test/helpers/messages_helper_test.rb
index f648827..488d72a 100644
--- a/test/helpers/messages_helper_test.rb
+++ b/test/helpers/messages_helper_test.rb
@@ -51,6 +51,17 @@ class MessagesHelperTest < ActionView::TestCase
     assert_no_match %r{poster=|/representations/}, presentation
   end
 
+  test "message_presentation shows a video whose frame was drawn but whose poster wasn't made without one" do
+    message = attachment_message("alpha-centuri.mov", "video/quicktime", processed: false)
+    message.attachment.preview(format: :jpg).processed
+    assert message.attachment.preview(:poster).processed?
+
+    presentation = view.message_presentation(message.reload)
+
+    assert_match %r{<video[^>]+src="[^"]*alpha-centuri\.mov"}, presentation
+    assert_no_match %r{poster=|/representations/}, presentation
+  end
+
   private
     def attachment_message(file, content_type, processed:)
       attributes = { creator: users(:jason), client_message_id: "0015", attachment: fixture_file_upload(file, content_type) }