diff --git a/config/settings.yml b/config/settings.yml
index 6077dcd3..751ec55f 100755
--- a/config/settings.yml
+++ b/config/settings.yml
@@ -1,7 +1,7 @@
 ad_plugin:
   discourse_adplugin_enabled:
     client: true
-    default: true
+    default: false
   no_ads_for_personal_messages:
     client: true
     default: true
diff --git a/db/migrate/20250721192553_enable_adplugin_if_already_installed.rb b/db/migrate/20250721192553_enable_adplugin_if_already_installed.rb
new file mode 100644
index 00000000..69179b67
--- /dev/null
+++ b/db/migrate/20250721192553_enable_adplugin_if_already_installed.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class EnableAdpluginIfAlreadyInstalled < ActiveRecord::Migration[7.2]
+  def up
+    installed_at = DB.query_single(<<~SQL)&.first
+      SELECT created_at FROM schema_migration_details WHERE version='20190603112536'
+    SQL
+
+    if installed_at && installed_at < 1.hour.ago
+      # The plugin was installed before we changed it to be disabled-by-default
+      # Therefore, if there is no existing database value, enable the plugin
+      execute <<~SQL
+        INSERT INTO site_settings(name, data_type, value, created_at, updated_at)
+        VALUES('discourse_adplugin_enabled', 5, 't', NOW(), NOW())
+        ON CONFLICT (name) DO NOTHING
+      SQL
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end
diff --git a/spec/models/house_ad_setting_spec.rb b/spec/models/house_ad_setting_spec.rb
index 9043aaae..1432e2fb 100644
--- a/spec/models/house_ad_setting_spec.rb
+++ b/spec/models/house_ad_setting_spec.rb
@@ -3,6 +3,8 @@
 describe AdPlugin::HouseAdSetting do
   let(:defaults) { AdPlugin::HouseAdSetting::DEFAULTS }
 
+  before { enable_current_plugin }
+
   describe ".all" do
     subject { AdPlugin::HouseAdSetting.all }
 
diff --git a/spec/models/house_ad_spec.rb b/spec/models/house_ad_spec.rb
index f3492aa2..d2977412 100644
--- a/spec/models/house_ad_spec.rb
+++ b/spec/models/house_ad_spec.rb
@@ -9,6 +9,8 @@
     }
   end
 
+  before { enable_current_plugin }
+
   def create_anon_ad
     AdPlugin::HouseAd.create(
       name: "anon-ad",
diff --git a/spec/requests/house_ad_controller_spec.rb b/spec/requests/house_ad_controller_spec.rb
index 3069fe4e..9f2b16c4 100644
--- a/spec/requests/house_ad_controller_spec.rb
+++ b/spec/requests/house_ad_controller_spec.rb
@@ -16,6 +16,8 @@
     )
   end
 
+  before { enable_current_plugin }
+
   describe "#update" do
     context "when used by admins" do
       before { sign_in(admin) }
diff --git a/spec/requests/house_ad_settings_controller_spec.rb b/spec/requests/house_ad_settings_controller_spec.rb
index bfc7605b..26f130a3 100644
--- a/spec/requests/house_ad_settings_controller_spec.rb
+++ b/spec/requests/house_ad_settings_controller_spec.rb
@@ -3,7 +3,10 @@
 describe AdPlugin::HouseAdSettingsController do
   let(:admin) { Fabricate(:admin) }
 
-  before { AdPlugin::HouseAd.create(name: "Banner", html: "<p>Banner</p>") }
+  before do
+    enable_current_plugin
+    AdPlugin::HouseAd.create(name: "Banner", html: "<p>Banner</p>")
+  end
 
   describe "update" do
     let(:valid_params) { { value: "Banner" } }
diff --git a/spec/requests/site_controller_spec.rb b/spec/requests/site_controller_spec.rb
index fced5d43..fb5b36a3 100644
--- a/spec/requests/site_controller_spec.rb
+++ b/spec/requests/site_controller_spec.rb
@@ -3,7 +3,6 @@
 RSpec.describe SiteController do
   fab!(:group)
   fab!(:private_category) { Fabricate(:private_category, group: group) }
-
   fab!(:user)
   fab!(:group_2) { Fabricate(:group) }
   fab!(:user_with_group) { Fabricate(:user, group_ids: [group.id]) }
@@ -75,6 +74,7 @@
   end
 
   before do
+    enable_current_plugin
     AdPlugin::HouseAdSetting.update(
       "topic_list_top",
       "logged-in-ad|anon-ad|everyone-ad|logged-in-ad-with-category|logged-in-ad-with-group|everyone-group-ad",
diff --git a/spec/serializer/current_user_serializer_spec.rb b/spec/serializer/current_user_serializer_spec.rb
index 53ac5b55..f5da55ef 100644
--- a/spec/serializer/current_user_serializer_spec.rb
+++ b/spec/serializer/current_user_serializer_spec.rb
@@ -14,7 +14,7 @@
 
   let(:admin_serializer) { described_class.new(admin, scope: Guardian.new(admin), root: false) }
 
-  before { SiteSetting.discourse_adplugin_enabled = true }
+  before { enable_current_plugin }
 
   describe "#adsense" do
     it "is displayed for TL0 by default" do
diff --git a/spec/system/admin_house_ad_spec.rb b/spec/system/admin_house_ad_spec.rb
index 4e046983..e3f9b422 100644
--- a/spec/system/admin_house_ad_spec.rb
+++ b/spec/system/admin_house_ad_spec.rb
@@ -11,7 +11,10 @@
     )
   end
 
-  before { sign_in(admin) }
+  before do
+    enable_current_plugin
+    sign_in(admin)
+  end
 
   describe "when visiting the page for creating new ads" do
     it "has the visibility checkboxes on by default" do