diff --git a/libethcore/BlockInfo.cpp b/libethcore/BlockInfo.cpp
index 8726ebe95..fec010c2d 100644
--- a/libethcore/BlockInfo.cpp
+++ b/libethcore/BlockInfo.cpp
@@ -191,7 +191,7 @@ u256 BlockInfo::calculateDifficulty(BlockInfo const& _parent) const
 	if (!parentHash)
 		return c_genesisDifficulty;
 	else
-		return timestamp >= _parent.timestamp + (c_protocolVersion == 49 ? 5 : 8) ? _parent.difficulty - (_parent.difficulty >> 10) : (_parent.difficulty + (_parent.difficulty >> 10));
+		return max<u256>(1024, timestamp >= _parent.timestamp + (c_protocolVersion == 49 ? 5 : 8) ? _parent.difficulty - (_parent.difficulty >> 10) : (_parent.difficulty + (_parent.difficulty >> 10)));
 }
 
 void BlockInfo::verifyParent(BlockInfo const& _parent) const