diff --git a/libraries/chain/fork_database.cpp b/libraries/chain/fork_database.cpp
index 85c9500d..482b27c3 100644
--- a/libraries/chain/fork_database.cpp
+++ b/libraries/chain/fork_database.cpp
@@ -85,7 +85,7 @@ void  fork_database::_push_block(const item_ptr& item)
    else if( item->num > _head->num )
    {
       _head = item;
-      auto  min_num = _head->num - _max_size;
+      uint32_t min_num = _head->num - std::min( _max_size, _head->num );
 //      ilog( "min block in fork DB ${n}, max_size: ${m}", ("n",min_num)("m",_max_size) );
       auto& num_idx = _index.get<block_num>();
       while( num_idx.size() && (*num_idx.begin())->num < min_num )