diff --git a/cashu/mint/db/write.py b/cashu/mint/db/write.py
index 13d8445d..42a602e0 100644
--- a/cashu/mint/db/write.py
+++ b/cashu/mint/db/write.py
@@ -181,16 +181,16 @@ async def _set_melt_quote_pending(self, quote: MeltQuote) -> MeltQuote:
         quote_copy = quote.copy()
         async with self.db.get_connection(
             lock_table="melt_quotes",
-            lock_select_statement=f"checking_id='{quote.checking_id}'",
+            lock_select_statement=f"quote='{quote.quote}'",
         ) as conn:
             # get melt quote from db and check if it is already pending
             quote_db = await self.crud.get_melt_quote(
-                checking_id=quote.checking_id, db=self.db, conn=conn
+                quote_id=quote.quote, db=self.db, conn=conn
             )
             if not quote_db:
                 raise TransactionError("Melt quote not found.")
-            # if quote_db.pending:
-            #     raise TransactionError("Melt quote already pending.")
+            if quote_db.pending:
+                raise TransactionError("Melt quote already pending.")
             # set the quote as pending
             quote_copy.state = MeltQuoteState.pending
             await self.crud.update_melt_quote(quote=quote_copy, db=self.db, conn=conn)
diff --git a/cashu/mint/ledger.py b/cashu/mint/ledger.py
index df01cf21..a48bfc7d 100644
--- a/cashu/mint/ledger.py
+++ b/cashu/mint/ledger.py
@@ -626,7 +626,6 @@ async def melt_quote(
         mint_quote = await self.crud.get_mint_quote(request=request, db=self.db)
         if mint_quote:
             payment_quote = self.create_internal_melt_quote(mint_quote, melt_quote)
-
         else:
             # not internal
             # verify that the backend supports mpp if the quote request has an amount
@@ -894,7 +893,6 @@ async def melt(
             proofs, quote_id=melt_quote.quote
         )
         previous_state = melt_quote.state
-        # Warning: _set_melt_quote_pending does NOT protect against race conditions (it does not throw an error)
         melt_quote = await self.db_write._set_melt_quote_pending(melt_quote)
         try:
             # if the melt corresponds to an internal mint, mark both as paid