diff --git a/app/routes/shared/formular.server.ts b/app/routes/shared/formular.server.ts
index fa5e5dea9..c976f88d8 100644
--- a/app/routes/shared/formular.server.ts
+++ b/app/routes/shared/formular.server.ts
@@ -40,6 +40,7 @@ import { updateMainSession } from "~/services/session.server/updateSessionInHead
 import { validateFormData } from "~/services/validation/validateFormData.server";
 import { getButtonNavigationProps } from "~/util/buttonProps";
 import { interpolateDeep } from "~/util/fillTemplate";
+import { filterFormData } from "~/util/filterFormData";
 
 const structureCmsContent = (
   formPageContent: z.infer<CollectionSchemas["form-flow-pages"]>,
@@ -214,11 +215,7 @@ export const action = async ({ request }: ActionFunctionArgs) => {
   const cookieHeader = request.headers.get("Cookie");
   const flowSession = await getSession(cookieHeader);
   const formData = await request.formData();
-
-  // Note: This also reduces same-named fields to the last entry
-  const relevantFormData = Object.fromEntries(
-    Array.from(formData.entries()).filter(([key]) => !key.startsWith("_")),
-  );
+  const relevantFormData = filterFormData(formData);
 
   if (formData.get("_action") === "delete") {
     try {
diff --git a/app/routes/shared/vorabcheck.server.ts b/app/routes/shared/vorabcheck.server.ts
index e2ad682a9..302b5e8d9 100644
--- a/app/routes/shared/vorabcheck.server.ts
+++ b/app/routes/shared/vorabcheck.server.ts
@@ -27,6 +27,7 @@ import { updateMainSession } from "~/services/session.server/updateSessionInHead
 import { validateFormData } from "~/services/validation/validateFormData.server";
 import { getButtonNavigationProps } from "~/util/buttonProps";
 import { interpolateDeep } from "~/util/fillTemplate";
+import { filterFormData } from "~/util/filterFormData";
 
 export const loader = async ({
   params,
@@ -135,11 +136,7 @@ export const action = async ({ request }: ActionFunctionArgs) => {
   const flowSession = await sessionManager.getSession(cookieHeader);
   const formData = await request.formData();
 
-  // Note: This also reduces same-named fields to the last entry
-  const relevantFormData = Object.fromEntries(
-    Array.from(formData.entries()).filter(([key]) => !key.startsWith("_")),
-  );
-
+  const relevantFormData = filterFormData(formData);
   const validationResult = await validateFormData(flowId, relevantFormData);
   if (validationResult.error)
     return validationError(
diff --git a/app/util/__test__/filterFormData.test.ts b/app/util/__test__/filterFormData.test.ts
new file mode 100644
index 000000000..691874352
--- /dev/null
+++ b/app/util/__test__/filterFormData.test.ts
@@ -0,0 +1,24 @@
+import { filterFormData } from "../filterFormData";
+
+describe("filterFormData", () => {
+  it("creates a object with data", () => {
+    const formData = new FormData();
+    formData.append("a", "1");
+    formData.append("b", "2");
+    expect(filterFormData(formData)).toEqual({ a: "1", b: "2" });
+  });
+
+  it("filters out entries starting with underscore", () => {
+    const formData = new FormData();
+    formData.append("a", "1");
+    formData.append("_b", "2");
+    expect(filterFormData(formData)).toEqual({ a: "1" });
+  });
+
+  it("filters out repeated entries", () => {
+    const formData = new FormData();
+    formData.append("a", "1");
+    formData.append("a", "2");
+    expect(filterFormData(formData)).toEqual({ a: "2" });
+  });
+});
diff --git a/app/util/filterFormData.ts b/app/util/filterFormData.ts
new file mode 100644
index 000000000..be6b7a9cf
--- /dev/null
+++ b/app/util/filterFormData.ts
@@ -0,0 +1,5 @@
+export const filterFormData = (formData: FormData) =>
+  // Note: fromEntries() reduces same-named form fields to the last one
+  Object.fromEntries(
+    Array.from(formData.entries()).filter(([key]) => !key.startsWith("_")),
+  );