diff --git a/include/bitcoin/database/impl/query/translate.ipp b/include/bitcoin/database/impl/query/translate.ipp
index 6b474b5b..47fbfd6a 100644
--- a/include/bitcoin/database/impl/query/translate.ipp
+++ b/include/bitcoin/database/impl/query/translate.ipp
@@ -199,10 +199,10 @@ header_link CLASS::to_parent(const header_link& link) const NOEXCEPT
 }
 
 TEMPLATE
-header_link CLASS::to_block(const tx_link& link) const NOEXCEPT
+header_link CLASS::to_block(const tx_link& key) const NOEXCEPT
 {
     table::strong_tx::record strong{};
-    if (!store_.strong_tx.find(link, strong) || !strong.positive)
+    if (!store_.strong_tx.find(key, strong) || !strong.positive)
         return {};
 
     // Terminal implies not strong (not in block).
@@ -216,6 +216,8 @@ header_link CLASS::to_block(const tx_link& link) const NOEXCEPT
 TEMPLATE
 inline strong_pair CLASS::to_strong(const hash_digest& tx_hash) const NOEXCEPT
 {
+    // Iteration of tx is necessary because there may be duplicates.
+    // Only top block (strong) association for given tx instance is considered.
     auto it = store_.tx.it(tx_hash);
     strong_pair strong{ {}, it.self() };
     if (!it)
diff --git a/include/bitcoin/database/query.hpp b/include/bitcoin/database/query.hpp
index cb5fd0cc..7fc5e735 100644
--- a/include/bitcoin/database/query.hpp
+++ b/include/bitcoin/database/query.hpp
@@ -272,7 +272,7 @@ class query
 
     /// block/tx to block/s (reverse navigation)
     header_link to_parent(const header_link& link) const NOEXCEPT;
-    header_link to_block(const tx_link& link) const NOEXCEPT;
+    header_link to_block(const tx_link& key) const NOEXCEPT;
 
     /// output to spenders (reverse navigation)
     spend_links to_spenders(const point& prevout) const NOEXCEPT;