diff --git a/src/main.cpp b/src/main.cpp
index 0b878b245..9e7cd3b60 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -4706,7 +4706,7 @@ bool CheckBlock(int32_t *futureblockp,int32_t height,CBlockIndex *pindex,const C
         int32_t i,j,rejects=0,lastrejects=0;
         //fprintf(stderr,"put block's tx into mempool\n");
         // Copy all non Z-txs in mempool to temporary mempool because there can be tx in local mempool that make the block invalid.
-        LOCK(mempool.cs);
+        LOCK2(cs_main,mempool.cs);
         //fprintf(stderr, "starting... mempoolsize.%ld\n",mempool.size());
         list<CTransaction> transactionsToRemove;
         BOOST_FOREACH(const CTxMemPoolEntry& e, mempool.mapTx) {