diff --git a/src/main.cpp b/src/main.cpp
index baad7fc050..613eeff227 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -740,17 +740,14 @@ bool CheckTransaction(const CTransaction& tx, CValidationState &state)
     return true;
 }
 
-CAmount GetMinRelayFee(const CTransaction& tx, unsigned int nBytes, bool fAllowFree)
+CAmount GetMinRelayFee(const CTransaction& tx, const CTxMemPool& pool, unsigned int nBytes, bool fAllowFree)
 {
-    {
-        LOCK(mempool.cs);
-        uint256 hash = tx.GetHash();
-        double dPriorityDelta = 0;
-        CAmount nFeeDelta = 0;
-        mempool.ApplyDeltas(hash, dPriorityDelta, nFeeDelta);
-        if (dPriorityDelta > 0 || nFeeDelta > 0)
-            return 0;
-    }
+    uint256 hash = tx.GetHash();
+    double dPriorityDelta = 0;
+    CAmount nFeeDelta = 0;
+    pool.ApplyDeltas(hash, dPriorityDelta, nFeeDelta);
+    if (dPriorityDelta > 0 || nFeeDelta > 0)
+        return 0;
 
     CAmount nMinFee = ::minRelayTxFee.GetFee(nBytes);
 
@@ -879,11 +876,11 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
         CAmount nFees = nValueIn-nValueOut;
         double dPriority = view.GetPriority(tx, chainActive.Height());
 
-        CTxMemPoolEntry entry(tx, nFees, GetTime(), dPriority, chainActive.Height(), mempool.HasNoInputsOf(tx));
+        CTxMemPoolEntry entry(tx, nFees, GetTime(), dPriority, chainActive.Height(), pool.HasNoInputsOf(tx));
         unsigned int nSize = entry.GetTxSize();
 
         // Don't accept it if it can't get into a block
-        CAmount txMinFee = GetMinRelayFee(tx, nSize, true);
+        CAmount txMinFee = GetMinRelayFee(tx, pool, nSize, true);
         if (fLimitFree && nFees < txMinFee)
             return state.DoS(0, false, REJECT_INSUFFICIENTFEE, "insufficient fee", false,
                 strprintf("%d < %d", nFees, txMinFee));
diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index 57bb284602..aa5aec0556 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -735,10 +735,10 @@ void CTxMemPool::PrioritiseTransaction(const uint256 hash, const string strHash,
     LogPrintf("PrioritiseTransaction: %s priority += %f, fee += %d\n", strHash, dPriorityDelta, FormatMoney(nFeeDelta));
 }
 
-void CTxMemPool::ApplyDeltas(const uint256 hash, double &dPriorityDelta, CAmount &nFeeDelta)
+void CTxMemPool::ApplyDeltas(const uint256 hash, double &dPriorityDelta, CAmount &nFeeDelta) const
 {
     LOCK(cs);
-    std::map<uint256, std::pair<double, CAmount> >::iterator pos = mapDeltas.find(hash);
+    std::map<uint256, std::pair<double, CAmount> >::const_iterator pos = mapDeltas.find(hash);
     if (pos == mapDeltas.end())
         return;
     const std::pair<double, CAmount> &deltas = pos->second;
diff --git a/src/txmempool.h b/src/txmempool.h
index 635b66fb85..cee1a146da 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -83,7 +83,7 @@ public:
 
     const CTransaction& GetTx() const { return this->tx; }
     double GetPriority(unsigned int currentHeight) const;
-    CAmount GetFee() const { return nFee; }
+    const CAmount& GetFee() const { return nFee; }
     size_t GetTxSize() const { return nTxSize; }
     int64_t GetTime() const { return nTime; }
     unsigned int GetHeight() const { return nHeight; }
@@ -371,7 +371,7 @@ public:
 
     /** Affect CreateNewBlock prioritisation of transactions */
     void PrioritiseTransaction(const uint256 hash, const std::string strHash, double dPriorityDelta, const CAmount& nFeeDelta);
-    void ApplyDeltas(const uint256 hash, double &dPriorityDelta, CAmount &nFeeDelta);
+    void ApplyDeltas(const uint256 hash, double &dPriorityDelta, CAmount &nFeeDelta) const;
     void ClearPrioritisation(const uint256 hash);
 
 public: