diff --git a/src/main.cpp b/src/main.cpp
index 366f77d21..e08787d56 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -403,7 +403,7 @@ namespace {
         
         if (!state->hashLastUnknownBlock.IsNull()) {
             BlockMap::iterator itOld = mapBlockIndex.find(state->hashLastUnknownBlock);
-            if (itOld != mapBlockIndex.end() && itOld->second->chainPower > CChainPower())
+            if (itOld != mapBlockIndex.end() && itOld->second != 0 && (itOld->second->chainPower > CChainPower()))
             {
                 if (state->pindexBestKnownBlock == NULL || itOld->second->chainPower >= state->pindexBestKnownBlock->chainPower)
                     state->pindexBestKnownBlock = itOld->second;