diff --git a/include/bitcoin/database/impl/query/confirm.ipp b/include/bitcoin/database/impl/query/confirm.ipp
index 25c543e6..d5ba23d5 100644
--- a/include/bitcoin/database/impl/query/confirm.ipp
+++ b/include/bitcoin/database/impl/query/confirm.ipp
@@ -283,25 +283,21 @@ inline error::error_t CLASS::unspent_duplicates(const tx_link& link,
     if (!ctx.is_enabled(system::chain::flags::bip30_rule))
         return error::success;
 
-    // Self should be strong but was not identified.
     const auto coinbases = to_strongs(get_tx_key(link));
     if (coinbases.empty())
         return error::integrity;
 
-    // Only self was found (optimization).
     if (is_one(coinbases.size()))
         return error::success;
 
-    // All but one (self) must be confirmed spent or coinbase is unspent.
-    size_t strong_unspent{};
-    for (const auto& coinbase: coinbases)
-        for (spend::pt::integer out{}; out < output_count(coinbase.tx); ++out)
-            if (!spent_prevout(spend::compose(coinbase.tx, out)) &&
-                is_one(strong_unspent++))
+    // bip30: all (but self) must be confirmed spent or dup invalid (cb only).
+    size_t unspent{};
+    for (const auto& cb: coinbases)
+        for (index out{}; out < output_count(cb.tx); ++out)
+            if (!spent_prevout(spend::compose(cb.tx, out)) && is_one(unspent++))
                 return error::unspent_coinbase_collision;
 
-    // Only self should/must be unspent.
-    return is_zero(strong_unspent) ? error::integrity : error::success;
+    return is_zero(unspent) ? error::integrity : error::success;
 }
 
 TEMPLATE
diff --git a/include/bitcoin/database/impl/query/translate.ipp b/include/bitcoin/database/impl/query/translate.ipp
index 790a80d0..509c15b2 100644
--- a/include/bitcoin/database/impl/query/translate.ipp
+++ b/include/bitcoin/database/impl/query/translate.ipp
@@ -254,10 +254,8 @@ inline header_links CLASS::to_blocks(const tx_link& link) const NOEXCEPT
     block_txs strongs{};
     do
     {
-        if (!store_.strong_tx.get(it.self(), strong))
-            return {};
- 
-        if (!contains(strongs, strong))
+        if (store_.strong_tx.get(it.self(), strong) &&
+            !contains(strongs, strong))
             strongs.push_back(strong);
     }
     while(it.advance());
diff --git a/include/bitcoin/database/query.hpp b/include/bitcoin/database/query.hpp
index ac2b1229..81ac6160 100644
--- a/include/bitcoin/database/query.hpp
+++ b/include/bitcoin/database/query.hpp
@@ -73,6 +73,7 @@ class query
     using chain_state = system::chain::chain_state;
     using chain_state_ptr = system::chain::chain_state::ptr;
     using chain_context = system::chain::context;
+    using index = table::transaction::ix::integer;
     using sizes = std::pair<size_t, size_t>;
     using heights = std_vector<size_t>;
     using filter = system::data_chunk;