diff --git a/assets/js/p.js b/assets/js/p.js
index 83cbcae300..a634e133fe 100644
--- a/assets/js/p.js
+++ b/assets/js/p.js
@@ -58,7 +58,7 @@
         uid: uid,
         user_agent: window.navigator.userAgent,
         referrer: window.document.referrer,
-        screenWidth: window.innerWidth
+        screen_width: window.innerWidth
       }));
 
       request.onreadystatechange = function() {
diff --git a/assets/js/plausible.js b/assets/js/plausible.js
index 94e222bbaa..804ae1ea7f 100644
--- a/assets/js/plausible.js
+++ b/assets/js/plausible.js
@@ -58,7 +58,7 @@
         uid: uid,
         user_agent: window.navigator.userAgent,
         referrer: window.document.referrer,
-        screenWidth: window.innerWidth
+        screen_width: window.innerWidth
       }));
 
       request.onreadystatechange = function() {
diff --git a/lib/plausible_web/controllers/api/external_controller.ex b/lib/plausible_web/controllers/api/external_controller.ex
index ce9004762c..11fe92b1ac 100644
--- a/lib/plausible_web/controllers/api/external_controller.ex
+++ b/lib/plausible_web/controllers/api/external_controller.ex
@@ -63,11 +63,11 @@ defmodule PlausibleWeb.Api.ExternalController do
     end
   end
 
+  defp calculate_screen_size(nil) , do: nil
   defp calculate_screen_size(width) when width < 576, do: "Mobile"
   defp calculate_screen_size(width) when width < 992, do: "Tablet"
   defp calculate_screen_size(width) when width < 1440, do: "Laptop"
   defp calculate_screen_size(width) when width >= 1440, do: "Desktop"
-  defp calculate_screen_size(_) , do: nil
 
   defp clean_referrer(referrer) do
     uri = if referrer do
diff --git a/test/plausible_web/controllers/api/external_controller_test.exs b/test/plausible_web/controllers/api/external_controller_test.exs
index 6cb5457eab..28094aba3b 100644
--- a/test/plausible_web/controllers/api/external_controller_test.exs
+++ b/test/plausible_web/controllers/api/external_controller_test.exs
@@ -285,4 +285,22 @@ defmodule PlausibleWeb.Api.ExternalControllerTest do
     assert response(conn, 202) == ""
     assert pageview.screen_size == "Mobile"
   end
+
+  test "screen size is nil if screen_width is missing", %{conn: conn} do
+    params = %{
+      url: "http://gigride.live/",
+      new_visitor: true,
+      uid: UUID.uuid4()
+    }
+
+    conn = conn
+           |> put_req_header("content-type", "text/plain")
+           |> put_req_header("user-agent", @user_agent)
+           |> post("/api/page", Jason.encode!(params))
+
+    pageview = Repo.one(Plausible.Pageview)
+
+    assert response(conn, 202) == ""
+    assert pageview.screen_size == nil
+  end
 end