diff --git a/src/tl/unit_tests/tlVariantTests.cc b/src/tl/unit_tests/tlVariantTests.cc
index 58a7b0595..84ca9755b 100644
--- a/src/tl/unit_tests/tlVariantTests.cc
+++ b/src/tl/unit_tests/tlVariantTests.cc
@@ -28,6 +28,7 @@
 #include "tlTypeTraits.h"
 #include "tlUnitTest.h"
 
+#define _USE_MATH_DEFINES // for MSVC
 #include <cmath>
 #include <cstdio>
 #include <memory>