diff --git a/lnbits/core/views/payment_api.py b/lnbits/core/views/payment_api.py
index 5239c7454..7e92ea078 100644
--- a/lnbits/core/views/payment_api.py
+++ b/lnbits/core/views/payment_api.py
@@ -405,6 +405,8 @@ async def api_payment(payment_hash, x_api_key: str | None = Header(None)):
         payment = await update_pending_payment(payment)
     except Exception:
         if wallet and wallet.id == payment.wallet_id:
+            # do not expose the preimage of unpaid payments
+            payment.preimage = None
             return {"paid": False, "details": payment}
         return {"paid": False}
 
@@ -412,10 +414,15 @@ async def api_payment(payment_hash, x_api_key: str | None = Header(None)):
         return {
             "paid": payment.success,
             "status": f"{payment.status!s}",
-            "preimage": payment.preimage,
+            # only expose the preimage once the payment is actually successful
+            "preimage": payment.preimage if payment.success else None,
             "details": payment,
         }
-    return {"paid": payment.success, "preimage": payment.preimage}
+    return {
+        "paid": payment.success,
+        # only expose the preimage once the payment is actually successful
+        "preimage": payment.preimage if payment.success else None,
+    }
 
 
 @payment_router.post("/decode", status_code=HTTPStatus.OK)
diff --git a/tests/api/test_api.py b/tests/api/test_api.py
index 2401c71fe..9771b87a1 100644
--- a/tests/api/test_api.py
+++ b/tests/api/test_api.py
@@ -1,3 +1,4 @@
+import asyncio
 import hashlib
 from json import JSONDecodeError
 from unittest.mock import AsyncMock, Mock
@@ -371,6 +372,73 @@ async def test_check_payment_with_key(client, invoice: Payment, inkey_headers_fr
     assert "details" in response.json()
 
 
+# check GET /api/v1/payments/<hash>: preimage of an unpaid invoice must not leak
+@pytest.mark.anyio
+async def test_check_pending_payment_does_not_expose_preimage(
+    client, inkey_headers_from, inkey_headers_to, adminkey_headers_from
+):
+    # create an unpaid invoice (FakeWallet stores a valid preimage at creation)
+    data = await get_random_invoice_data()
+    response = await client.post("/api/v1/payments", json=data, headers=inkey_headers_to)
+    assert response.status_code == 201
+    unpaid = response.json()
+    payment_hash = unpaid["payment_hash"]
+
+    # unauthenticated request must not return the preimage
+    response = await client.get(f"/api/v1/payments/{payment_hash}")
+    assert response.status_code < 300
+    assert response.json()["paid"] is False
+    assert response.json()["preimage"] is None
+
+    # same for an invalid key
+    response = await client.get(
+        f"/api/v1/payments/{payment_hash}", headers={"X-Api-Key": "invalid_key"}
+    )
+    assert response.json()["paid"] is False
+    assert response.json()["preimage"] is None
+
+    # a valid key of a different (non-owning) wallet scopes the lookup
+    # to that wallet and therefore yields 404, leaking nothing at all
+    response = await client.get(
+        f"/api/v1/payments/{payment_hash}", headers=inkey_headers_from
+    )
+    assert response.status_code == 404
+
+    # expired unpaid invoices must not leak the preimage either
+    expiry_data = await get_random_invoice_data()
+    expiry_data["expiry"] = 1
+    response = await client.post(
+        "/api/v1/payments", json=expiry_data, headers=inkey_headers_to
+    )
+    assert response.status_code == 201
+    expired_hash = response.json()["payment_hash"]
+    await asyncio.sleep(2)
+    response = await client.get(f"/api/v1/payments/{expired_hash}")
+    assert response.json()["paid"] is False
+    assert response.json()["preimage"] is None
+
+    # after payment the preimage is exposed again as proof of payment
+    response = await client.post(
+        "/api/v1/payments",
+        json={"out": True, "bolt11": unpaid["bolt11"]},
+        headers=adminkey_headers_from,
+    )
+    assert response.status_code < 300
+    # internal payments settle asynchronously, give the listener a moment
+    preimage = None
+    paid = False
+    for _ in range(10):
+        response = await client.get(f"/api/v1/payments/{payment_hash}")
+        paid = response.json()["paid"]
+        preimage = response.json()["preimage"]
+        if paid:
+            break
+        await asyncio.sleep(0.5)
+    assert paid is True
+    assert preimage is not None
+    assert hashlib.sha256(bytes.fromhex(preimage)).hexdigest() == payment_hash
+
+
 # check POST /api/v1/payments: payment with wrong key type
 @pytest.mark.anyio
 async def test_pay_invoice_wrong_key(client, invoice, adminkey_headers_from):