diff --git a/src/main.cpp b/src/main.cpp
index 640fbac8b..875cd6734 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -49,7 +49,7 @@ int64 CTransaction::nMinTxFee = 10000;  // Override with -mintxfee
 /** Fees smaller than this (in satoshi) are considered zero fee (for relaying) */
 int64 CTransaction::nMinRelayTxFee = 10000;
 
-CMedianFilter<int> cPeerBlockCounts(8, 0); // Amount of blocks that other nodes claim to have
+static CMedianFilter<int> cPeerBlockCounts(8, 0); // Amount of blocks that other nodes claim to have
 
 map<uint256, CBlock*> mapOrphanBlocks;
 multimap<uint256, CBlock*> mapOrphanBlocksByPrev;
@@ -3396,8 +3396,9 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
 
         LogPrintf("receive version message: version %d, blocks=%d, us=%s, them=%s, peer=%s\n", pfrom->nVersion, pfrom->nStartingHeight, addrMe.ToString().c_str(), addrFrom.ToString().c_str(), pfrom->addr.ToString().c_str());
 
-        LOCK(cs_main);
         AddTimeData(pfrom->addr, nTime);
+
+        LOCK(cs_main);
         cPeerBlockCounts.input(pfrom->nStartingHeight);
     }
 
diff --git a/src/util.cpp b/src/util.cpp
index 9ee1ad5f5..085df8a7d 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -80,7 +80,6 @@ bool fServer = false;
 string strMiscWarning;
 bool fNoListen = false;
 bool fLogTimestamps = false;
-CMedianFilter<int64> vTimeOffsets(200,0);
 volatile bool fReopenDebugLog = false;
 
 // Init OpenSSL library multithreading support
@@ -1305,10 +1304,12 @@ void SetMockTime(int64 nMockTimeIn)
     nMockTime = nMockTimeIn;
 }
 
+static CCriticalSection cs_nTimeOffset;
 static int64 nTimeOffset = 0;
 
 int64 GetTimeOffset()
 {
+    LOCK(cs_nTimeOffset);
     return nTimeOffset;
 }
 
@@ -1321,12 +1322,14 @@ void AddTimeData(const CNetAddr& ip, int64 nTime)
 {
     int64 nOffsetSample = nTime - GetTime();
 
+    LOCK(cs_nTimeOffset);
     // Ignore duplicates
     static set<CNetAddr> setKnown;
     if (!setKnown.insert(ip).second)
         return;
 
     // Add data
+    static CMedianFilter<int64> vTimeOffsets(200,0);
     vTimeOffsets.input(nOffsetSample);
     LogPrintf("Added time data, samples %d, offset %+"PRI64d" (%+"PRI64d" minutes)\n", vTimeOffsets.size(), nOffsetSample, nOffsetSample/60);
     if (vTimeOffsets.size() >= 5 && vTimeOffsets.size() % 2 == 1)