diff --git a/client/src/locales/de/translation.json b/client/src/locales/de/translation.json
index e02c702e..d9e2b6b3 100644
--- a/client/src/locales/de/translation.json
+++ b/client/src/locales/de/translation.json
@@ -219,6 +219,7 @@
   "a.Personen, die du begleitest": "Personen, die du begleitest ",
   "a.Persönliche Informationen": "Persönliche Informationen",
   "a.PLZ": "PLZ",
+  "a.Postleizahl hat das falsche Format": "Postleizahl hat das falsche Format",
   "a.Praxisauftrag": "Praxisauftrag",
   "a.Praxisaufträge anschauen": "Praxisaufträge anschauen",
   "a.Praxisbildner": "Praxisbildner",
diff --git a/client/src/locales/fr/translation.json b/client/src/locales/fr/translation.json
index 3de4022c..ef3c306a 100644
--- a/client/src/locales/fr/translation.json
+++ b/client/src/locales/fr/translation.json
@@ -219,6 +219,7 @@
   "a.Personen, die du begleitest": "Personnes que tu accompagnes",
   "a.Persönliche Informationen": "Informations personnelles",
   "a.PLZ": "Code postal",
+  "a.Postleizahl hat das falsche Format": "Le code postal n'a pas le bon format",
   "a.Praxisauftrag": "Exercice pratique",
   "a.Praxisaufträge anschauen": "Voir les missions pratiques",
   "a.Praxisbildner": "Formateur pratique",
diff --git a/client/src/locales/it/translation.json b/client/src/locales/it/translation.json
index 30f04667..da81b106 100644
--- a/client/src/locales/it/translation.json
+++ b/client/src/locales/it/translation.json
@@ -219,6 +219,7 @@
   "a.Personen, die du begleitest": "Persone che accompagni",
   "a.Persönliche Informationen": "Informazioni personali",
   "a.PLZ": "CAP",
+  "a.Postleizahl hat das falsche Format": "Il codice postale ha un formato sbagliato",
   "a.Praxisauftrag": "Lavoro pratico",
   "a.Praxisaufträge anschauen": "Visualizzare gli incarichi pratici",
   "a.Praxisbildner": "Formatore pratico",
diff --git a/client/src/pages/onboarding/vv/CheckoutAddress.vue b/client/src/pages/onboarding/vv/CheckoutAddress.vue
index 89d71557..cb1b7b72 100644
--- a/client/src/pages/onboarding/vv/CheckoutAddress.vue
+++ b/client/src/pages/onboarding/vv/CheckoutAddress.vue
@@ -15,6 +15,7 @@ import { useEntities } from "@/services/entities";
 import { getLocalSessionKey } from "@/statistics";
 import { type User, useUserStore } from "@/stores/user";
 import { normalizeSwissPhoneNumber, validatePhoneNumber } from "@/utils/phone";
+import { validatePostalCode } from "@/utils/postalcode";
 import { useTranslation } from "i18next-vue";
 import log from "loglevel";
 import { computed, ref, watch } from "vue";
@@ -129,6 +130,8 @@ function validateAddress() {
 
   if (!address.value.postal_code) {
     formErrors.value.personal.push(t("a.PLZ"));
+  } else if (!validatePostalCode(address.value.postal_code)) {
+    formErrors.value.personal.push(t("a.Postleizahl hat das falsche Format"));
   }
 
   if (!address.value.city) {
@@ -172,6 +175,8 @@ function validateAddress() {
 
     if (!address.value.organisation_postal_code) {
       formErrors.value.company.push(t("a.PLZ"));
+    } else if (!validatePostalCode(address.value.organisation_postal_code)) {
+      formErrors.value.personal.push(t("a.Postleizahl hat das falsche Format"));
     }
 
     if (!address.value.organisation_city) {
diff --git a/client/src/utils/postalcode.ts b/client/src/utils/postalcode.ts
new file mode 100644
index 00000000..59fdac69
--- /dev/null
+++ b/client/src/utils/postalcode.ts
@@ -0,0 +1,10 @@
+export function validatePostalCode(input: string) {
+  // Remove non-ASCII characters
+  // eslint-disable-next-line no-control-regex
+  input = input.replace(/[^\x00-\x7F]/g, "");
+  if (input.length < 4) {
+    return false;
+  }
+  const regex = /^[0-9]+$/;
+  return regex.test(input);
+}