diff --git a/libraries/chain/account_evaluator.cpp b/libraries/chain/account_evaluator.cpp
index 1f29bb0a..f34af18f 100644
--- a/libraries/chain/account_evaluator.cpp
+++ b/libraries/chain/account_evaluator.cpp
@@ -62,6 +62,13 @@ void_result account_create_evaluator::do_evaluate( const account_create_operatio
       FC_ASSERT( !op.extensions.value.owner_special_authority.valid() );
       FC_ASSERT( !op.extensions.value.active_special_authority.valid() );
    }
+   if( d.head_block_time() < HARDFORK_599_TIME )
+   {
+      FC_ASSERT( !op.extensions.value.null_ext.valid() );
+      FC_ASSERT( !op.extensions.value.owner_special_authority.valid() );
+      FC_ASSERT( !op.extensions.value.active_special_authority.valid() );
+      FC_ASSERT( !op.extensions.value.buyback_options.valid() );
+   }
 
    FC_ASSERT( d.find_object(op.options.voting_account), "Invalid proxy account specified." );
    FC_ASSERT( fee_paying_account->is_lifetime_member(), "Only Lifetime members may register an account." );
@@ -223,6 +230,12 @@ void_result account_update_evaluator::do_evaluate( const account_update_operatio
       FC_ASSERT( !o.extensions.value.owner_special_authority.valid() );
       FC_ASSERT( !o.extensions.value.active_special_authority.valid() );
    }
+   if( d.head_block_time() < HARDFORK_599_TIME )
+   {
+      FC_ASSERT( !o.extensions.value.null_ext.valid() );
+      FC_ASSERT( !o.extensions.value.owner_special_authority.valid() );
+      FC_ASSERT( !o.extensions.value.active_special_authority.valid() );
+   }
 
    const auto& chain_params = d.get_global_properties().parameters;
 
diff --git a/libraries/chain/hardfork.d/599.hf b/libraries/chain/hardfork.d/599.hf
new file mode 100644
index 00000000..71f7e94e
--- /dev/null
+++ b/libraries/chain/hardfork.d/599.hf
@@ -0,0 +1,4 @@
+// #599 Unpacking of extension is incorrect
+#ifndef HARDFORK_599_TIME
+#define HARDFORK_599_TIME (fc::time_point_sec( 1458061200 ))
+#endif