diff --git a/test/src/unit-diagnostics.cpp b/test/src/unit-diagnostics.cpp
index c465cda6e..a835dff32 100644
--- a/test/src/unit-diagnostics.cpp
+++ b/test/src/unit-diagnostics.cpp
@@ -34,6 +34,7 @@ SOFTWARE.
 #endif
 
 #define JSON_DIAGNOSTICS 1
+#define JSON_TESTS_PRIVATE
 
 #include <nlohmann/json.hpp>
 using nlohmann::json;