diff --git a/app/jobs/scheduled/clean_up_uploads.rb b/app/jobs/scheduled/clean_up_uploads.rb
index a3d9f1e55e7..770ff7144b8 100644
--- a/app/jobs/scheduled/clean_up_uploads.rb
+++ b/app/jobs/scheduled/clean_up_uploads.rb
@@ -38,7 +38,6 @@ module Jobs
           encoded_sha = Base62.encode(upload.sha1.hex)
           next if ReviewableQueuedPost.pending.where("payload->>'raw' LIKE '%#{upload.sha1}%' OR payload->>'raw' LIKE '%#{encoded_sha}%'").exists?
           next if Draft.where("data LIKE '%#{upload.sha1}%' OR data LIKE '%#{encoded_sha}%'").exists?
-          next if ThemeSetting.where(data_type: ThemeSetting.types[:upload]).where("value LIKE ?", "%#{upload.sha1}%").exists?
           if defined?(ChatMessage) &&
               ChatMessage.where("message LIKE ? OR message LIKE ?", "%#{upload.sha1}%", "%#{encoded_sha}%").exists?
             next
diff --git a/app/models/upload.rb b/app/models/upload.rb
index f03883783cb..d0611ba84af 100644
--- a/app/models/upload.rb
+++ b/app/models/upload.rb
@@ -90,6 +90,12 @@ class Upload < ActiveRecord::Base
       .where("g.flair_upload_id IS NULL")
       .joins("LEFT JOIN badges b ON b.image_upload_id = uploads.id")
       .where("b.image_upload_id IS NULL")
+      .joins(<<~SQL)
+        LEFT JOIN theme_settings ts
+        ON NULLIF(ts.value, '')::integer = uploads.id
+        AND ts.data_type = #{ThemeSetting.types[:upload].to_i}
+      SQL
+      .where("ts.value IS NULL")
 
     if SiteSetting.selectable_avatars.present?
       scope = scope.where.not(id: SiteSetting.selectable_avatars.map(&:id))
diff --git a/db/migrate/20210914152002_update_value_on_theme_setting_for_upload_type.rb b/db/migrate/20210914152002_update_value_on_theme_setting_for_upload_type.rb
new file mode 100644
index 00000000000..00807694c3c
--- /dev/null
+++ b/db/migrate/20210914152002_update_value_on_theme_setting_for_upload_type.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+class UpdateValueOnThemeSettingForUploadType < ActiveRecord::Migration[6.1]
+  def up
+    execute <<~SQL
+      UPDATE theme_settings
+      SET value = (SELECT id FROM uploads WHERE uploads.url = theme_settings.value)
+      WHERE data_type = 6
+    SQL
+  end
+
+  def down
+    execute <<~SQL
+      UPDATE theme_settings
+      SET value = (SELECT url FROM uploads WHERE uploads.id = theme_settings.value)
+      WHERE data_type = 6
+    SQL
+  end
+end
diff --git a/lib/theme_settings_manager.rb b/lib/theme_settings_manager.rb
index 7ebbcc21418..2e905717b7c 100644
--- a/lib/theme_settings_manager.rb
+++ b/lib/theme_settings_manager.rb
@@ -22,7 +22,7 @@ class ThemeSettingsManager
   end
 
   def value
-    has_record? ? db_record.value : @default
+    has_record? ? db_record.value : default
   end
 
   def type_name
@@ -174,9 +174,48 @@ class ThemeSettingsManager
 
   class Upload < self
     def value
-      val = super
-      Discourse.store.cdn_url(val)
+      cdn_url(super)
     end
 
+    def default
+      upload_id = default_upload_id
+      return if upload_id.blank?
+
+      cdn_url(upload_id)
+    end
+
+    def value=(new_value)
+      if new_value.present?
+        if new_value == default
+          new_value = default_upload_id
+        else
+          upload = ::Upload.find_by(url: new_value)
+          new_value = upload.id if upload.present?
+        end
+      end
+
+      super(new_value)
+    end
+
+    private
+
+    def cdn_url(upload_id)
+      return if upload_id.blank?
+
+      upload = ::Upload.find_by_id(upload_id.to_i)
+      return if upload.blank?
+
+      Discourse.store.cdn_url(upload.url)
+    end
+
+    def default_upload_id
+      theme_field = theme.theme_fields.find_by(
+        name: @default,
+        type_id: ThemeField.types[:theme_upload_var]
+      )
+      return if theme_field.blank?
+
+      theme_field.upload_id
+    end
   end
 end
diff --git a/spec/components/theme_settings_manager_spec.rb b/spec/components/theme_settings_manager_spec.rb
index 2659883fd40..70cde6bc0c3 100644
--- a/spec/components/theme_settings_manager_spec.rb
+++ b/spec/components/theme_settings_manager_spec.rb
@@ -149,4 +149,24 @@ describe ThemeSettingsManager do
       expect(list_setting.list_type).to eq("compact")
     end
   end
+
+  context "Upload" do
+    let!(:upload) { Fabricate(:upload) }
+
+    it "saves the upload id" do
+      upload_setting = find_by_name(:upload_setting)
+      upload_setting.value = upload.url
+      theme.reload
+
+      expect(ThemeSetting.exists?(theme_id: theme.id, name: "upload_setting", value: upload.id.to_s)).to be_truthy
+    end
+
+    it "returns the CDN URL" do
+      upload_setting = find_by_name(:upload_setting)
+      upload_setting.value = upload.url
+      theme.reload
+
+      expect(upload_setting.value).to eq(Discourse.store.cdn_url(upload.url))
+    end
+  end
 end
diff --git a/spec/jobs/clean_up_uploads_spec.rb b/spec/jobs/clean_up_uploads_spec.rb
index 219b2f4c19e..093a760cc3d 100644
--- a/spec/jobs/clean_up_uploads_spec.rb
+++ b/spec/jobs/clean_up_uploads_spec.rb
@@ -288,7 +288,7 @@ describe Jobs::CleanUpUploads do
   it "does not delete theme setting uploads" do
     theme = Fabricate(:theme)
     theme_upload = fabricate_upload
-    ThemeSetting.create!(theme: theme, data_type: ThemeSetting.types[:upload], value: theme_upload.url, name: "my_setting_name")
+    ThemeSetting.create!(theme: theme, data_type: ThemeSetting.types[:upload], value: theme_upload.id.to_s, name: "my_setting_name")
 
     Jobs::CleanUpUploads.new.execute(nil)
 
diff --git a/spec/models/theme_spec.rb b/spec/models/theme_spec.rb
index 90550ff2ce7..a47571e444b 100644
--- a/spec/models/theme_spec.rb
+++ b/spec/models/theme_spec.rb
@@ -542,7 +542,7 @@ HTML
         default: ""
     YAML
 
-    ThemeSetting.create!(theme: theme, data_type: ThemeSetting.types[:upload], value: upload.url, name: "my_upload")
+    ThemeSetting.create!(theme: theme, data_type: ThemeSetting.types[:upload], value: upload.id.to_s, name: "my_upload")
     theme.save!
 
     json = JSON.parse(cached_settings(theme.id))