diff --git a/stepmania/src/archutils/Win32/arch_setup.h b/stepmania/src/archutils/Win32/arch_setup.h
index 370bfd4fe6..51d992198a 100644
--- a/stepmania/src/archutils/Win32/arch_setup.h
+++ b/stepmania/src/archutils/Win32/arch_setup.h
@@ -36,5 +36,9 @@
 #undef max
 #define NOMINMAX /* make sure Windows doesn't try to define this */
 
+/* Windows is missing some basic math functions: */
+#define NEED_TRUNCF
+#define NEED_ROUNDF
+
 #endif