diff --git a/electrum/lnworker.py b/electrum/lnworker.py
index 7be4673a1..7e074afbb 100644
--- a/electrum/lnworker.py
+++ b/electrum/lnworker.py
@@ -845,7 +845,7 @@ class LNWallet(LNWorker):
         self.lnwatcher = LNWatcher(self)
         self.lnrater: LNRater = None
         self.payment_info = self.db.get_dict('lightning_payments')     # RHASH -> amount, direction, is_paid
-        self.preimages = self.db.get_dict('lightning_preimages')   # RHASH -> preimage
+        self._preimages = self.db.get_dict('lightning_preimages')   # RHASH -> preimage
         self._bolt11_cache = {}
         # note: this sweep_address is only used as fallback; as it might result in address-reuse
         self.logs = defaultdict(list)  # type: Dict[str, List[HtlcLog]]  # key is RHASH  # (not persisted)
@@ -2286,13 +2286,13 @@ class LNWallet(LNWorker):
     def save_preimage(self, payment_hash: bytes, preimage: bytes, *, write_to_disk: bool = True):
         if sha256(preimage) != payment_hash:
             raise Exception("tried to save incorrect preimage for payment_hash")
-        self.preimages[payment_hash.hex()] = preimage.hex()
+        self._preimages[payment_hash.hex()] = preimage.hex()
         if write_to_disk:
             self.wallet.save_db()
 
     def get_preimage(self, payment_hash: bytes) -> Optional[bytes]:
         assert isinstance(payment_hash, bytes), f"expected bytes, but got {type(payment_hash)}"
-        preimage_hex = self.preimages.get(payment_hash.hex())
+        preimage_hex = self._preimages.get(payment_hash.hex())
         if preimage_hex is None:
             return None
         preimage_bytes = bytes.fromhex(preimage_hex)
@@ -2300,6 +2300,10 @@ class LNWallet(LNWorker):
             raise Exception("found incorrect preimage for payment_hash")
         return preimage_bytes
 
+    def get_preimage_hex(self, payment_hash: str) -> Optional[str]:
+        preimage_bytes = self.get_preimage(bytes.fromhex(payment_hash)) or b""
+        return preimage_bytes.hex() or None
+
     def get_payment_info(self, payment_hash: bytes) -> Optional[PaymentInfo]:
         """returns None if payment_hash is a payment we are forwarding"""
         key = payment_hash.hex()
diff --git a/electrum/plugins/nwc/nwcserver.py b/electrum/plugins/nwc/nwcserver.py
index be77a661f..9d96f424e 100644
--- a/electrum/plugins/nwc/nwcserver.py
+++ b/electrum/plugins/nwc/nwcserver.py
@@ -534,7 +534,7 @@ class NWCServer(Logger, EventListener):
         if direction:
             response['result']['type'] = direction
         if status == PR_PAID:
-            response['result']['preimage'] = self.wallet.lnworker.preimages.get(invoice.rhash, "not found")
+            response['result']['preimage'] = self.wallet.lnworker.get_preimage_hex(invoice.rhash) or "not found"
         self.logger.debug(f"lookup_invoice response: {response}")
         await self.send_encrypted_response(request_event.pubkey, json.dumps(response), request_event.id)
 
@@ -731,7 +731,7 @@ class NWCServer(Logger, EventListener):
             "amount": request.get_amount_msat(),
             "created_at": request.time,
             "expires_at": request.get_expiration_date(),
-            "preimage": self.wallet.lnworker.preimages.get(request.rhash, "not found"),
+            "preimage": self.wallet.lnworker.get_preimage_hex(invoice.rhash) or "not found",
             "metadata": {},
             "fees_paid": 0
         }
@@ -760,7 +760,7 @@ class NWCServer(Logger, EventListener):
             "type": "outgoing",
             "invoice": invoice.lightning_invoice or "",
             "description": invoice.message,
-            "preimage": self.wallet.lnworker.preimages.get(key, "not found"),
+            "preimage": self.wallet.lnworker.get_preimage_hex(invoice.rhash) or "not found",
             "payment_hash": invoice.rhash,
             "amount": invoice.get_amount_msat(),
             "created_at": invoice.time,
diff --git a/electrum/submarine_swaps.py b/electrum/submarine_swaps.py
index ece5f20fa..d9785d6e9 100644
--- a/electrum/submarine_swaps.py
+++ b/electrum/submarine_swaps.py
@@ -392,7 +392,7 @@ class SwapManager(Logger):
                     if preimage:
                         swap.preimage = preimage
                         self.logger.info(f'found preimage: {preimage.hex()}')
-                        self.lnworker.preimages[swap.payment_hash.hex()] = preimage.hex()
+                        self.lnworker.save_preimage(swap.payment_hash, preimage)
                     else:
                         # this is our refund tx
                         if spent_height > 0:
diff --git a/tests/test_lnpeer.py b/tests/test_lnpeer.py
index b5624167f..083ddea01 100644
--- a/tests/test_lnpeer.py
+++ b/tests/test_lnpeer.py
@@ -206,7 +206,7 @@ class MockLNWallet(Logger, EventListener, NetworkRetryManager[LNPeerAddr]):
         self.active_forwardings = {}
         self.forwarding_failures = {}
         self.inflight_payments = set()
-        self.preimages = {}
+        self._preimages = {}
         self.stopping_soon = False
         self.downstream_to_upstream_htlc = {}
         self.dont_settle_htlcs = {}
@@ -593,7 +593,7 @@ class TestPeer(ElectrumTestCase):
     def prepare_recipient(self, w2, payment_hash, test_hold_invoice, test_failure):
         if not test_hold_invoice and not test_failure:
             return
-        preimage = bytes.fromhex(w2.preimages.pop(payment_hash.hex()))
+        preimage = bytes.fromhex(w2._preimages.pop(payment_hash.hex()))
         if test_hold_invoice:
             async def cb(payment_hash):
                 if not test_failure: