diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index cbe4878932a4..127d3f308c27 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -2323,6 +2323,12 @@ TransactionError CWallet::FillPSBT(PartiallySignedTransaction& psbtx, bool& comp
     }
     const PrecomputedTransactionData txdata = PrecomputePSBTData(psbtx);
     LOCK(cs_wallet);
+    if (sign && IsLocked()) {
+        // A mixing-only unlock still exposes private keys to the
+        // ScriptPubKeyMans, so refuse to sign here and report zero signed inputs.
+        sign = false;
+        n_signed = nullptr;
+    }
     // Get all of the previous transactions
     for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
         const CTxIn& txin = psbtx.tx->vin[i];
diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
index 7cd93f499aab..bc2c3bb719bf 100755
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -77,6 +77,10 @@ def run_test(self):
         unsigned_tx = self.nodes[0].walletprocesspsbt(psbtx, False)
         assert_equal(unsigned_tx['complete'], False)
 
+        # Unlocking for mixing only must not allow signing either
+        self.nodes[0].walletpassphrase("password", 1000000, True)
+        assert_equal(self.nodes[0].send({self.nodes[2].getnewaddress(): 10})['complete'], False)
+
         self.nodes[0].walletpassphrase(passphrase="password", timeout=1000000)
 
         # Sign the transaction but don't finalize