diff --git a/src/main.cpp b/src/main.cpp
index 676c77cdc..cb07c181b 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -4310,7 +4310,7 @@ bool CheckBlock(int32_t *futureblockp,int32_t height,CBlockIndex *pindex,const C
     int invalidtxs = 0;
     BOOST_FOREACH(const CTxMemPoolEntry& e, tmpmempool.mapTx) {
         const CTransaction &tx = e.GetTx();
-        if ( myAddtomempool(tx) == false ) // this happens if there were invalid txs in the local mempool, on block arrival.
+        if ( myAddtomempool(tx) == false ) // this happens if there were invalid txs in the local mempool, on block arrival, used to make the block invalid.
             invalidtxs++;
         fprintf(stderr, "added mempool tx back to mempool\n");
     }