diff --git a/libraries/chain/account_evaluator.cpp b/libraries/chain/account_evaluator.cpp
index 8ff2efcd..9eed05e1 100644
--- a/libraries/chain/account_evaluator.cpp
+++ b/libraries/chain/account_evaluator.cpp
@@ -191,18 +191,6 @@ object_id_type account_create_evaluator::do_apply( const account_create_operatio
       obj.active           = o.active;
       obj.options          = o.options;
 
-      if (!obj.options.extensions.value.num_son.valid())
-      {
-         obj.options.extensions.value.num_son = []{
-                        flat_map<sidechain_type, uint16_t> num_son;
-                        for(const auto& active_sidechain_type : all_sidechain_types){
-                           num_son[active_sidechain_type] = 0;
-                        }
-                        return num_son;
-                     }();
-
-      }
-
       obj.statistics = d.create<account_statistics_object>([&obj](account_statistics_object& s){
                            s.owner = obj.id;
                            s.name = obj.name;
@@ -343,18 +331,6 @@ void_result account_update_evaluator::do_apply( const account_update_operation&
       }
       if( o.new_options ) a.options = *o.new_options;
 
-      if (!a.options.extensions.value.num_son.valid())
-      {
-         a.options.extensions.value.num_son = []{
-            flat_map<sidechain_type, uint16_t> num_son;
-            for(const auto& active_sidechain_type : all_sidechain_types){
-               num_son[active_sidechain_type] = 0;
-            }
-            return num_son;
-         }();
-
-      }
-
       if( o.extensions.value.owner_special_authority.valid() )
       {
          a.owner_special_authority = *(o.extensions.value.owner_special_authority);
diff --git a/libraries/chain/db_maint.cpp b/libraries/chain/db_maint.cpp
index e4ccc45d..397e9ccd 100644
--- a/libraries/chain/db_maint.cpp
+++ b/libraries/chain/db_maint.cpp
@@ -2382,7 +2382,24 @@ void database::perform_chain_maintenance(const signed_block& next_block, const g
 
             if ( opinion_account.options.extensions.value.num_son.valid() )
             {
-               for(const auto& num_sidechain_son : *opinion_account.options.extensions.value.num_son) {
+               auto active_sidechains = active_sidechain_types(d.head_block_time());
+               auto num_son_map = *opinion_account.options.extensions.value.num_son;
+
+               if ( num_son_map.size() != active_sidechains.size())
+               {
+                  for (const auto& num_sidechain_son : num_son_map)
+                  {
+                     FC_ASSERT(active_sidechains.find(num_sidechain_son.first) != active_sidechains.end());
+                     active_sidechains.erase(num_sidechain_son.first);
+                  }
+
+                  for (auto missing_num_son : active_sidechains)
+                  {
+                     num_son_map[missing_num_son] = 0;
+                  }
+               }
+
+               for(const auto& num_sidechain_son : num_son_map) {
                   const auto sidechain = num_sidechain_son.first;
                   const auto& num_son = num_sidechain_son.second;
                   if (num_son <= props.parameters.maximum_son_count()) {
diff --git a/libraries/wallet/wallet.cpp b/libraries/wallet/wallet.cpp
index e1363b0b..41522613 100644
--- a/libraries/wallet/wallet.cpp
+++ b/libraries/wallet/wallet.cpp
@@ -2838,8 +2838,24 @@ public:
          if (!votes_removed)
             FC_THROW("Account ${account} is already not voting for SON ${son}", ("account", voting_account)("son", son));
       }
+      auto active_sidechains = active_sidechain_types(time_point::now());
+      auto num_son_map = *voting_account_object.options.extensions.value.num_son;
+
+      if ( num_son_map.size() != active_sidechains.size())
+      {
+         for (const auto& num_sidechain_son : num_son_map)
+         {
+            FC_ASSERT(active_sidechains.find(num_sidechain_son.first) != active_sidechains.end());
+            active_sidechains.erase(num_sidechain_son.first);
+         }
+
+         for (auto missing_num_son : active_sidechains)
+         {
+            num_son_map[missing_num_son] = 0;
+         }
+      }
       FC_ASSERT( voting_account_object.options.extensions.value.num_son.valid() , "Invalid son number" );
-      (*voting_account_object.options.extensions.value.num_son)[sidechain] = desired_number_of_sons;
+      num_son_map[sidechain] = desired_number_of_sons;
 
       account_update_operation account_update_op;
       account_update_op.account = voting_account_object.id;