diff --git a/backend/src/routes/resources/main.ts b/backend/src/routes/resources/main.ts
index e72036b..419ab42 100644
--- a/backend/src/routes/resources/main.ts
+++ b/backend/src/routes/resources/main.ts
@@ -239,6 +239,13 @@ function isDateValue(value: any) {
 }
 
 function normalizeCreatedDocumentPayload(payload: Record<string, any>) {
+    if (Object.prototype.hasOwnProperty.call(payload, "customSurchargePercentage")) {
+        const customSurchargePercentage = Number(payload.customSurchargePercentage)
+        payload.customSurchargePercentage = Number.isFinite(customSurchargePercentage)
+            ? customSurchargePercentage
+            : 0
+    }
+
     const numberRelationFields = [
         "customer",
         "contact",
diff --git a/frontend/pages/createDocument/edit/[[id]].vue b/frontend/pages/createDocument/edit/[[id]].vue
index 54aface..85ff571 100644
--- a/frontend/pages/createDocument/edit/[[id]].vue
+++ b/frontend/pages/createDocument/edit/[[id]].vue
@@ -1701,6 +1701,7 @@ const saveSerialInvoice = async () => {
 const saveDocument = async (state, resetup = false) => {
 
   itemInfo.value.state = state
+  normalizeCustomSurchargePercentage()
 
   if (state !== "Entwurf") {
     console.log("???")
@@ -1870,7 +1871,14 @@ const checkCompatibilityWithInputPrice = () => {
   })
 }
 
+const normalizeCustomSurchargePercentage = () => {
+  const percentage = Number(itemInfo.value.customSurchargePercentage)
+  itemInfo.value.customSurchargePercentage = Number.isFinite(percentage) ? percentage : 0
+}
+
 const updateCustomSurcharge = () => {
+  normalizeCustomSurchargePercentage()
+
   itemInfo.value.rows.forEach(row => {
     if (!["pagebreak", "title", "text"].includes(row.mode) && isImportedAdvanceInvoiceRow(row)) {
       row.price = Number(row.inputPrice || 0)