diff --git a/app/controllers/graphs_controller.rb b/app/controllers/graphs_controller.rb
index 528c8d29..7ffcbebb 100644
--- a/app/controllers/graphs_controller.rb
+++ b/app/controllers/graphs_controller.rb
@@ -158,7 +158,7 @@ def monthly_ttd
                    .to_h
              end
            end
-    data = data.map { |k, v| [k, v.round(params[:round].to_i)] } if params[:round]
+    data = data.map { |k, v| [k, v&.round(params[:round].to_i)] } if params[:round]
     render json: data
   end