diff --git a/src/privatesend-server.cpp b/src/privatesend-server.cpp
index 9b03e95bbd..761ec9e1f0 100644
--- a/src/privatesend-server.cpp
+++ b/src/privatesend-server.cpp
@@ -18,6 +18,8 @@
 #include "utilmoneystr.h"
 #include "validation.h"
 
+#include "llmq/quorums_instantsend.h"
+
 CPrivateSendServer privateSendServer;
 
 void CPrivateSendServer::ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStream& vRecv, CConnman& connman)
@@ -217,7 +219,15 @@ void CPrivateSendServer::ProcessMessage(CNode* pfrom, const std::string& strComm
                 LogPrint("privatesend", "DSVIN -- txin=%s\n", txin.ToString());
 
                 Coin coin;
-                if (GetUTXOCoin(txin.prevout, coin)) {
+                auto mempoolTx = mempool.get(txin.prevout.hash);
+                if (mempoolTx != nullptr) {
+                    if (mempool.isSpent(txin.prevout) || !llmq::quorumInstantSendManager->IsLocked(txin.prevout.hash)) {
+                        LogPrintf("DSVIN -- spent or non-locked mempool input! txin=%s\n", txin.ToString());
+                        PushStatus(pfrom, STATUS_REJECTED, ERR_MISSING_TX, connman);
+                        return;
+                    }
+                    nValueIn += mempoolTx->vout[txin.prevout.n].nValue;
+                } else if (GetUTXOCoin(txin.prevout, coin)) {
                     nValueIn += coin.out.nValue;
                 } else {
                     LogPrintf("DSVIN -- missing input! txin=%s\n", txin.ToString());
diff --git a/src/privatesend.cpp b/src/privatesend.cpp
index e7b2e9efbb..f96f0dfba0 100644
--- a/src/privatesend.cpp
+++ b/src/privatesend.cpp
@@ -16,6 +16,8 @@
 #include "utilmoneystr.h"
 #include "validation.h"
 
+#include "llmq/quorums_instantsend.h"
+
 #include <string>
 
 bool CPrivateSendEntry::AddScriptSig(const CTxIn& txin)
@@ -238,11 +240,19 @@ bool CPrivateSend::IsCollateralValid(const CTransaction& txCollateral)
 
     for (const auto& txin : txCollateral.vin) {
         Coin coin;
-        if (!GetUTXOCoin(txin.prevout, coin)) {
+        auto mempoolTx = mempool.get(txin.prevout.hash);
+        if (mempoolTx != nullptr) {
+            if (mempool.isSpent(txin.prevout) || !llmq::quorumInstantSendManager->IsLocked(txin.prevout.hash)) {
+                LogPrint("privatesend", "CPrivateSend::IsCollateralValid -- spent or non-locked mempool input! txin=%s\n", txin.ToString());
+                return false;
+            }
+            nValueIn += mempoolTx->vout[txin.prevout.n].nValue;
+        } else if (GetUTXOCoin(txin.prevout, coin)) {
+            nValueIn += coin.out.nValue;
+        } else {
             LogPrint("privatesend", "CPrivateSend::IsCollateralValid -- Unknown inputs in collateral transaction, txCollateral=%s", txCollateral.ToString());
             return false;
         }
-        nValueIn += coin.out.nValue;
     }
 
     //collateral transactions are required to pay out a small fee to the miners