diff --git a/tests/basictest.cpp b/tests/basictest.cpp
index 7abcc9e..925b00c 100644
--- a/tests/basictest.cpp
+++ b/tests/basictest.cpp
@@ -26,6 +26,16 @@
 #if defined(__CYGWIN__) || defined(__MINGW32__) || defined(__MINGW64__) || defined(sun) || defined(__sun)
 #define FASTFLOAT_ODDPLATFORM 1
 #endif
+
+#if defined __has_include
+#if __has_include (<filesystem>)
+#else
+#define FASTFLOAT_ODDPLATFORM 1
+#endif
+#else
+#define FASTFLOAT_ODDPLATFORM 1
+#endif
+
 // C++ 17 because it is otherwise annoying to browse all files in a directory.
 // We also only run these tests on little endian systems.
 #if (FASTFLOAT_CPLUSPLUS >= 201703L) && (FASTFLOAT_IS_BIG_ENDIAN == 0) && !defined(FASTFLOAT_ODDPLATFORM)