diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 65b610f0e..1afb000ae 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -37,7 +37,8 @@ endif()
 add_library(test_main OBJECT src/unit.cpp)
 target_compile_definitions(test_main PUBLIC
     DOCTEST_CONFIG_SUPER_FAST_ASSERTS
-    JSON_TEST_KEEP_MACROS)
+    JSON_TEST_KEEP_MACROS
+    JSON_TEST_USING_MULTIPLE_HEADERS=$<BOOL:${JSON_MultipleHeaders}>)
 target_compile_features(test_main PRIVATE cxx_std_11)
 target_compile_options(test_main PUBLIC
     $<$<CXX_COMPILER_ID:MSVC>:/EHsc;$<$<CONFIG:Release>:/Od>>