diff --git a/include/bitcoin/system/chain/outpoint.hpp b/include/bitcoin/system/chain/outpoint.hpp
index 82f5fd7e04..d9b397e977 100644
--- a/include/bitcoin/system/chain/outpoint.hpp
+++ b/include/bitcoin/system/chain/outpoint.hpp
@@ -40,7 +40,7 @@ class BC_API outpoint
 
     static constexpr size_t serialized_size() NOEXCEPT
     {
-        return point::serialized_size() + sizeof(uint32_t);
+        return point::serialized_size() + sizeof(uint64_t);
     }
 
     /// Constructors.
diff --git a/test/chain/outpoint.cpp b/test/chain/outpoint.cpp
index 2831e86c14..4aaaffafcb 100644
--- a/test/chain/outpoint.cpp
+++ b/test/chain/outpoint.cpp
@@ -178,8 +178,8 @@ BOOST_AUTO_TEST_CASE(outpoint__is_null__default_null__true)
 
 BOOST_AUTO_TEST_CASE(outpoint__serialized_size__always__expected)
 {
-    static_assert(outpoint::serialized_size() == point::serialized_size() + sizeof(uint32_t));
-    BOOST_REQUIRE_EQUAL(outpoint::serialized_size(), point::serialized_size() + sizeof(uint32_t));
+    static_assert(outpoint::serialized_size() == point::serialized_size() + sizeof(uint64_t));
+    BOOST_REQUIRE_EQUAL(outpoint::serialized_size(), point::serialized_size() + sizeof(uint64_t));
 }
 
 // json