diff --git a/app/controllers/users/push_subscriptions_controller.rb b/app/controllers/users/push_subscriptions_controller.rb
index a3517a8..6b33452 100644
--- a/app/controllers/users/push_subscriptions_controller.rb
+++ b/app/controllers/users/push_subscriptions_controller.rb
@@ -28,15 +28,17 @@ class Users::PushSubscriptionsController < ApplicationController
 
     # A password change ends every session and subscription. A request that authenticated just before it mustn't
     # put one back, so the session is checked under the same write lock as the save, and the endpoint is looked up
-    # again there so two tabs posting at once register it once. Validation, which resolves the endpoint's address,
-    # runs before taking the lock.
+    # again there, past the query cache, so two tabs posting at once register it once. Validation, which resolves
+    # the endpoint's address, runs before taking the lock.
     def register_while_signed_in(subscription)
-      Push::Subscription.transaction do
-        if Session.exists?(Current.session.id)
-          if existing = @push_subscriptions.find_by(push_subscription_params)
-            existing.touch
-          else
-            subscription.save!(validate: false)
+      Push::Subscription.uncached do
+        Push::Subscription.transaction do
+          if Session.exists?(Current.session.id)
+            if existing = @push_subscriptions.find_by(push_subscription_params)
+              existing.touch
+            else
+              subscription.save!(validate: false)
+            end
           end
         end
       end
diff --git a/app/javascript/controllers/notifications_controller.js b/app/javascript/controllers/notifications_controller.js
index 3ce53a5..f7dfe7e 100644
--- a/app/javascript/controllers/notifications_controller.js
+++ b/app/javascript/controllers/notifications_controller.js
@@ -106,7 +106,8 @@ export default class extends Controller {
 
   async #syncPushSubscription(subscription) {
     const response = await post(this.subscriptionsUrlValue, { body: this.#extractJsonPayloadAsString(subscription), responseKind: "turbo-stream" })
-    if (!response.ok) subscription.unsubscribe()
+    // Only a refused endpoint is for good. A session signed out mid-request posts it again after signing in.
+    if (response.unprocessableEntity) subscription.unsubscribe()
   }
 
   async #requestPermissionAndSubscribe(registration) {
diff --git a/test/controllers/users/push_subscriptions_controller_test.rb b/test/controllers/users/push_subscriptions_controller_test.rb
index 7815626..cbfacb4 100644
--- a/test/controllers/users/push_subscriptions_controller_test.rb
+++ b/test/controllers/users/push_subscriptions_controller_test.rb
@@ -139,3 +139,33 @@ class Users::PushSubscriptionsControllerTest < ActionDispatch::IntegrationTest
       { "endpoint" => "https://fcm.googleapis.com/fcm/send/abc123", "p256dh_key" => "123", "auth_key" => "456" }
     end
 end
+
+class Users::PushSubscriptionsControllerForeignWriteTest < ActionDispatch::IntegrationTest
+  self.use_transactional_tests = false
+
+  setup do
+    sign_in :david
+    stub_web_push_dns_resolution
+  end
+
+  test "a subscription another connection registers while this one validates isn't registered twice" do
+    params = { "endpoint" => "https://fcm.googleapis.com/fcm/send/foreign", "p256dh_key" => "123", "auth_key" => "456" }
+    Push::Subscription.any_instance.stubs(:valid?).with { foreign_insert(params); true }.returns(true)
+
+    post user_push_subscriptions_url, params: { push_subscription: params }
+
+    assert_response :ok
+    assert_equal 1, Push::Subscription.where(endpoint: params["endpoint"]).count
+  end
+
+  private
+    def foreign_insert(params)
+      unless @inserted
+        SQLite3::Database.new(ActiveRecord::Base.connection_db_config.database) do |database|
+          database.execute "INSERT INTO push_subscriptions (user_id, endpoint, p256dh_key, auth_key, created_at, updated_at) " \
+            "VALUES (?, ?, ?, ?, datetime('now'), datetime('now'))", [ users(:david).id, *params.values ]
+        end
+        @inserted = true
+      end
+    end
+end