diff --git a/lnbits/core/models/payments.py b/lnbits/core/models/payments.py
index 7ed99d71..122f72aa 100644
--- a/lnbits/core/models/payments.py
+++ b/lnbits/core/models/payments.py
@@ -198,7 +198,7 @@ class CreateInvoice(BaseModel):
     internal: bool = False
     out: bool = True
     amount: float = Query(None, ge=0)
-    memo: str | None = None
+    memo: str | None = Query(None, max_length=640)
     description_hash: str | None = None
     unhashed_description: str | None = None
     expiry: int | None = None
diff --git a/lnbits/core/services/payments.py b/lnbits/core/services/payments.py
index bdc96801..8ec0612c 100644
--- a/lnbits/core/services/payments.py
+++ b/lnbits/core/services/payments.py
@@ -108,7 +108,7 @@ async def create_invoice(
     if not user_wallet:
         raise InvoiceError(f"Could not fetch wallet '{wallet_id}'.", status="failed")
 
-    invoice_memo = None if description_hash else memo
+    invoice_memo = None if description_hash else memo[:640]
 
     # use the fake wallet if the invoice is for internal use only
     funding_source = fake_wallet if internal else get_funding_source()