diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index 56437de93..15acafde6 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -472,6 +472,13 @@ bool CTxMemPool::addUnchecked(const uint256& hash, const CTxMemPoolEntry &entry,
         }
         mapProTxRefs.emplace(proTx.proTxHash, tx.GetHash());
         mapProTxBlsPubKeyHashes.emplace(proTx.pubKeyOperator.GetHash(), tx.GetHash());
+
+        auto dmn = deterministicMNManager->GetListAtChainTip().GetMN(proTx.proTxHash);
+        assert(dmn); // we should never get such a ProTx into the mempool
+        newit->validForProTxKey = ::SerializeHash(dmn->pdmnState->pubKeyOperator);
+        if (dmn->pdmnState->pubKeyOperator != proTx.pubKeyOperator) {
+            newit->isKeyChangeProTx = true;
+        }
     } else if (tx.nType == TRANSACTION_PROVIDER_UPDATE_REVOKE) {
         CProUpRevTx proTx;
         if (!GetTxPayload(tx, proTx)) {
@@ -479,6 +486,12 @@ bool CTxMemPool::addUnchecked(const uint256& hash, const CTxMemPoolEntry &entry,
             return false;
         }
         mapProTxRefs.emplace(proTx.proTxHash, tx.GetHash());
+        auto dmn = deterministicMNManager->GetListAtChainTip().GetMN(proTx.proTxHash);
+        assert(dmn); // we should never get such a ProTx into the mempool
+        newit->validForProTxKey = ::SerializeHash(dmn->pdmnState->pubKeyOperator);
+        if (dmn->pdmnState->pubKeyOperator != CBLSPublicKey()) {
+            newit->isKeyChangeProTx = true;
+        }
     }
 
     return true;
@@ -893,6 +906,24 @@ void CTxMemPool::removeProTxSpentCollateralConflicts(const CTransaction &tx)
     }
 }
 
+void CTxMemPool::removeProTxKeyChangedConflicts(const CTransaction &tx, const uint256& proTxHash, const uint256& newKeyHash)
+{
+    std::set<uint256> conflictingTxs;
+    for (auto its = mapProTxRefs.equal_range(proTxHash); its.first != its.second; ++its.first) {
+        auto txit = mapTx.find(its.first->second);
+        if (txit == mapTx.end()) {
+            continue;
+        }
+        if (txit->validForProTxKey != newKeyHash) {
+            conflictingTxs.emplace(txit->GetTx().GetHash());
+        }
+    }
+    for (const auto& txHash : conflictingTxs) {
+        auto& tx = mapTx.find(txHash)->GetTx();
+        removeRecursive(tx, MemPoolRemovalReason::CONFLICT);
+    }
+}
+
 void CTxMemPool::removeProTxConflicts(const CTransaction &tx)
 {
     removeProTxSpentCollateralConflicts(tx);
@@ -936,6 +967,15 @@ void CTxMemPool::removeProTxConflicts(const CTransaction &tx)
         }
 
         removeProTxPubKeyConflicts(tx, proTx.pubKeyOperator);
+        removeProTxKeyChangedConflicts(tx, proTx.proTxHash, ::SerializeHash(proTx.pubKeyOperator));
+    } else if (tx.nType == TRANSACTION_PROVIDER_UPDATE_REVOKE) {
+        CProUpRevTx proTx;
+        if (!GetTxPayload(tx, proTx)) {
+            LogPrintf("%s: ERROR: Invalid transaction payload, tx: %s", __func__, tx.ToString());
+            return;
+        }
+
+        removeProTxKeyChangedConflicts(tx, proTx.proTxHash, ::SerializeHash(CBLSPublicKey()));
     }
 }
 
@@ -1218,6 +1258,20 @@ TxMempoolInfo CTxMemPool::info(const uint256& hash) const
 
 bool CTxMemPool::existsProviderTxConflict(const CTransaction &tx) const {
     LOCK(cs);
+
+    auto hasKeyChangeInMempool = [&](const uint256& proTxHash) {
+        for (auto its = mapProTxRefs.equal_range(proTxHash); its.first != its.second; ++its.first) {
+            auto txit = mapTx.find(its.first->second);
+            if (txit == mapTx.end()) {
+                continue;
+            }
+            if (txit->isKeyChangeProTx) {
+                return true;
+            }
+        }
+        return false;
+    };
+
     if (tx.nType == TRANSACTION_PROVIDER_REGISTER) {
         CProRegTx proTx;
         if (!GetTxPayload(tx, proTx)) {
@@ -1243,8 +1297,33 @@ bool CTxMemPool::existsProviderTxConflict(const CTransaction &tx) const {
             LogPrintf("%s: ERROR: Invalid transaction payload, tx: %s", __func__, tx.ToString());
             return true; // i.e. can't decode payload == conflict
         }
+
+        // only allow one operator key change in the mempool
+        auto dmn = deterministicMNManager->GetListAtChainTip().GetMN(proTx.proTxHash);
+        assert(dmn); // this method should only be called with validated ProTxs
+        if (dmn->pdmnState->pubKeyOperator != proTx.pubKeyOperator) {
+            if (hasKeyChangeInMempool(proTx.proTxHash)) {
+                return true;
+            }
+        }
+
         auto it = mapProTxBlsPubKeyHashes.find(proTx.pubKeyOperator.GetHash());
         return it != mapProTxBlsPubKeyHashes.end() && it->second != proTx.proTxHash;
+    } else if (tx.nType == TRANSACTION_PROVIDER_UPDATE_REVOKE) {
+        CProUpRevTx proTx;
+        if (!GetTxPayload(tx, proTx)) {
+            LogPrintf("%s: ERROR: Invalid transaction payload, tx: %s", __func__, tx.ToString());
+            return true; // i.e. can't decode payload == conflict
+        }
+
+        // only allow one operator key change in the mempool
+        auto dmn = deterministicMNManager->GetListAtChainTip().GetMN(proTx.proTxHash);
+        assert(dmn); // this method should only be called with validated ProTxs
+        if (dmn->pdmnState->pubKeyOperator != CBLSPublicKey()) {
+            if (hasKeyChangeInMempool(proTx.proTxHash)) {
+                return true;
+            }
+        }
     }
     return false;
 }
diff --git a/src/txmempool.h b/src/txmempool.h
index 1362c8064..e88edf80f 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -162,6 +162,10 @@ public:
     unsigned int GetSigOpCountWithAncestors() const { return nSigOpCountWithAncestors; }
 
     mutable size_t vTxHashesIdx; //!< Index in mempool's vTxHashes
+
+    // If this is a proTx, this will be the hash of the key for which this ProTx was valid
+    mutable uint256 validForProTxKey;
+    mutable bool isKeyChangeProTx{false};
 };
 
 // Helpers for modifying CTxMemPool::mapTx, which is a boost multi_index.
@@ -586,6 +590,7 @@ public:
     void removeProTxPubKeyConflicts(const CTransaction &tx, const CBLSPublicKey &pubKey);
     void removeProTxCollateralConflicts(const CTransaction &tx, const COutPoint &collateralOutpoint);
     void removeProTxSpentCollateralConflicts(const CTransaction &tx);
+    void removeProTxKeyChangedConflicts(const CTransaction &tx, const uint256& proTxHash, const uint256& newKeyHash);
     void removeProTxConflicts(const CTransaction &tx);
     void removeForBlock(const std::vector<CTransactionRef>& vtx, unsigned int nBlockHeight);