diff --git a/tests/unit_tests/serialization.cpp b/tests/unit_tests/serialization.cpp
index bd53b009..fd0807b5 100644
--- a/tests/unit_tests/serialization.cpp
+++ b/tests/unit_tests/serialization.cpp
@@ -26,10 +26,12 @@ struct Struct
   char blob[8];
 };
 
-
-std::ostream& operator <<(std::ostream& o, const currency::signature_v& v)
+namespace currency
 {
-  return o;
+  ostream& operator<<(ostream& stream, [[maybe_unused]] const currency::signature_v& signature)
+  {
+    return stream;
+  }
 }
 
 template <class Archive>
@@ -902,4 +904,4 @@ TEST(Serialization, versioning2)
   r = perform_test_ser_vers<A_v3>(a_3);
   ASSERT_TRUE(r);
 
-}
\ No newline at end of file
+}