diff --git a/src/wallet/coinjoin.cpp b/src/wallet/coinjoin.cpp
index 0a2b6705d49b..d4f12cad2713 100644
--- a/src/wallet/coinjoin.cpp
+++ b/src/wallet/coinjoin.cpp
@@ -284,10 +284,13 @@ int CWallet::GetRealOutpointCoinJoinRounds(const COutPoint& outpoint, int nRound
     const CWalletTx* wtx{GetWalletTx(outpoint.hash)};
 
     if (wtx == nullptr || wtx->tx == nullptr) {
-        // no such tx in this wallet
-        *nRoundsRef = -1;
+        // No such tx in this wallet: don't memoize the result, the wallet may
+        // still learn about the tx later (e.g. a rescan in progress) and nothing
+        // invalidates the cache when it does. RPCs feed user-supplied outpoints
+        // into this via IsFullyMixed, so this path is reachable for any outpoint.
+        mapOutpointRoundsCache.erase(pair.first);
         WalletCJLogPrint(this, "%s FAILED    %-70s %3d\n", __func__, outpoint.ToStringShort(), -1);
-        return *nRoundsRef;
+        return -1;
     }
 
     // bounds check
diff --git a/src/wallet/test/coinjoin_tests.cpp b/src/wallet/test/coinjoin_tests.cpp
index 582593382a1c..4fcec9982b0b 100644
--- a/src/wallet/test/coinjoin_tests.cpp
+++ b/src/wallet/test/coinjoin_tests.cpp
@@ -552,6 +552,29 @@ BOOST_FIXTURE_TEST_CASE(coinjoin_rebalance_rounds_reset_tests, CTransactionBuild
     }
 }
 
+BOOST_FIXTURE_TEST_CASE(coinjoin_rounds_cache_unknown_tx_tests, CTransactionBuilderTestSetup)
+{
+    constexpr CAmount nDenomAmount{10000100}; // 0.100001 DASH
+    BOOST_REQUIRE(CoinJoin::IsDenominatedAmount(nDenomAmount));
+
+    CompactTallyItem tallyItem = GetTallyItem({nDenomAmount});
+    const CScript scriptOurs = GetScriptForRawPubKey(coinbaseKey.GetPubKey());
+
+    CMutableTransaction mtxMix;
+    mtxMix.vin.emplace_back(tallyItem.outpoints[0]);
+    mtxMix.vout.emplace_back(nDenomAmount, scriptOurs);
+    const COutPoint outpointMixed{mtxMix.GetHash(), 0};
+
+    // Queried before the wallet knows the tx, the way RPCs do for user-supplied
+    // preset inputs: unknown, reported as -1
+    BOOST_CHECK_EQUAL(wallet->GetRealOutpointCoinJoinRounds(outpointMixed), -1);
+
+    // Once the wallet learns the tx its rounds are computed from it; the miss
+    // above must not stick in mapOutpointRoundsCache
+    BOOST_REQUIRE(wallet->AddToWallet(MakeTransactionRef(mtxMix), TxStateInMempool{}));
+    BOOST_CHECK_EQUAL(wallet->GetRealOutpointCoinJoinRounds(outpointMixed), 1);
+}
+
 BOOST_FIXTURE_TEST_CASE(CTransactionBuilderTest, CTransactionBuilderTestSetup)
 {
     // NOTE: Mock wallet version is FEATURE_BASE which means that it uses uncompressed pubkeys