diff --git a/libraries/chain/db_block.cpp b/libraries/chain/db_block.cpp
index b571f88748..6c6e3f1d6a 100644
--- a/libraries/chain/db_block.cpp
+++ b/libraries/chain/db_block.cpp
@@ -131,8 +131,19 @@ bool database::_push_block(const signed_block& new_block)
    uint32_t skip = get_node_properties().skip_flags;
    if( !(skip&skip_fork_db) )
    {
-      /// TODO: if the block is greater than the head block and before the next maitenance interval
-      // verify that the block signer is in the current set of active witnesses.
+
+      // If the block is greater than the head block and before the next maintenance interval
+      if (new_block.block_num() > head_block_num()
+            && new_block.timestamp < get_dynamic_global_properties().next_maintenance_time )
+      {
+         // make sure the block signer is in the current set of active witnesses
+         const auto& witnesses = get_global_properties().active_witnesses;
+         witnesses.find(new_block.witness);
+         if ( witnesses.find(new_block.witness) == witnesses.end() )
+         {
+            FC_THROW_EXCEPTION(fc::assert_exception, "database::_push_block: Block witness not in list of active witnesses.");
+         }
+      }
 
       shared_ptr<fork_item> new_head = _fork_db.push_block(new_block);
       //If the head block from the longest chain does not build off of the current head, we need to switch forks.