diff --git a/lib/plausible_web/email.ex b/lib/plausible_web/email.ex
index c132f7d52ed6074b6417e0074cd2b6713fdf55fc..ab1c5870ad8bcad9c12fffd33d263138f2e12c41 100644
--- a/lib/plausible_web/email.ex
+++ b/lib/plausible_web/email.ex
@@ -119,7 +119,7 @@ defmodule PlausibleWeb.Email do
     base_email()
     |> to(user)
     |> tag("over-limit")
-    |> subject("You have outgrown your Plausible subscription tier")
+    |> subject("[Action required] You have outgrown your Plausible subscription tier")
     |> render("over_limit.html", %{
       user: user,
       usage: usage,
diff --git a/test/workers/check_usage_test.exs b/test/workers/check_usage_test.exs
index fa92f4662f8f9dcd0c1bb4f8afbe76178821d9a8..c5458458300f6d69ea3822e4ade5187e9f437b86 100644
--- a/test/workers/check_usage_test.exs
+++ b/test/workers/check_usage_test.exs
@@ -69,7 +69,7 @@ defmodule Plausible.Workers.CheckUsageTest do
 
     assert_email_delivered_with(
       to: [user],
-      subject: "You have outgrown your Plausible subscription tier"
+      subject: "[Action required] You have outgrown your Plausible subscription tier"
     )
 
     assert Repo.reload(user).grace_period_end == Timex.shift(Timex.today(), days: 7)
@@ -156,7 +156,7 @@ defmodule Plausible.Workers.CheckUsageTest do
 
       assert_email_delivered_with(
         to: [user],
-        subject: "You have outgrown your Plausible subscription tier"
+        subject: "[Action required] You have outgrown your Plausible subscription tier"
       )
     end
 
@@ -202,7 +202,7 @@ defmodule Plausible.Workers.CheckUsageTest do
 
       assert_email_delivered_with(
         to: [user],
-        subject: "You have outgrown your Plausible subscription tier"
+        subject: "[Action required] You have outgrown your Plausible subscription tier"
       )
     end
   end