diff --git a/modules/templates/helper.go b/modules/templates/helper.go
index b6c170cc3a..15b36d5dc8 100644
--- a/modules/templates/helper.go
+++ b/modules/templates/helper.go
@@ -173,7 +173,8 @@ func NewFuncMap() template.FuncMap {
 			return !setting.ImportLocalPaths
 		},
 		"ThemeName": func(user *user_model.User) string {
-			if user == nil {
+			// Guest user may not be nil on some pages, e.g. in org pages, so user.Theme check is also needed
+			if user == nil || user.Theme == "" {
 				return setting.UI.DefaultTheme
 			}
 			return user.Theme
diff --git a/tests/integration/org_test.go b/tests/integration/org_test.go
index ddfaf2fa55..7766b76ef6 100644
--- a/tests/integration/org_test.go
+++ b/tests/integration/org_test.go
@@ -1,4 +1,5 @@
 // Copyright 2019 The Gitea Authors. All rights reserved.
+// Copyright 2024 The Forgejo Authors. All rights reserved.
 // SPDX-License-Identifier: MIT
 
 package integration
@@ -54,6 +55,14 @@ func TestOrgRepos(t *testing.T) {
 	}
 }
 
+func TestPublicOrgHome(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	// Verify that in org pages, default theme get properly assigned to guest users
+	page := NewHTMLParser(t, MakeRequest(t, NewRequest(t, "GET", "/org41"), http.StatusOK).Body)
+	page.AssertElement(t, "html head link[rel='stylesheet'][href^='/assets/css/theme-forgejo-auto.css']", true)
+}
+
 func TestLimitedOrg(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()