diff --git a/lib/read_only_mixin.rb b/lib/read_only_mixin.rb
index 7775040aff4..74b88111ec3 100644
--- a/lib/read_only_mixin.rb
+++ b/lib/read_only_mixin.rb
@@ -38,8 +38,8 @@ module ReadOnlyMixin
   end
 
   def get_or_check_staff_writes_only_mode
-    check_readonly_mode if @readonly_mode.nil?
-    @readonly_mode
+    check_readonly_mode if @staff_writes_only_mode.nil?
+    @staff_writes_only_mode
   end
 
   def add_readonly_header
diff --git a/spec/requests/application_controller_spec.rb b/spec/requests/application_controller_spec.rb
index 86d34d8803c..56f414ad0cc 100644
--- a/spec/requests/application_controller_spec.rb
+++ b/spec/requests/application_controller_spec.rb
@@ -1332,5 +1332,27 @@ RSpec.describe ApplicationController do
         expect(JSON.parse(preloaded_json["visiblePlugins"])).to eq([])
       end
     end
+
+    describe "readonly serialization" do
+      it "serializes regular readonly mode correctly" do
+        Discourse.enable_readonly_mode(Discourse::USER_READONLY_MODE_KEY)
+
+        get "/latest"
+        expect(JSON.parse(preloaded_json["isReadOnly"])).to eq(true)
+        expect(JSON.parse(preloaded_json["isStaffWritesOnly"])).to eq(false)
+      ensure
+        Discourse.disable_readonly_mode(Discourse::USER_READONLY_MODE_KEY)
+      end
+
+      it "serializes staff readonly mode correctly" do
+        Discourse.enable_readonly_mode(Discourse::STAFF_WRITES_ONLY_MODE_KEY)
+
+        get "/latest"
+        expect(JSON.parse(preloaded_json["isReadOnly"])).to eq(true)
+        expect(JSON.parse(preloaded_json["isStaffWritesOnly"])).to eq(true)
+      ensure
+        Discourse.disable_readonly_mode(Discourse::STAFF_WRITES_ONLY_MODE_KEY)
+      end
+    end
   end
 end