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-rw-r--r--include/c99_math.h5
1 files changed, 5 insertions, 0 deletions
diff --git a/include/c99_math.h b/include/c99_math.h
index 5d4f5359db4..0a359ebb762 100644
--- a/include/c99_math.h
+++ b/include/c99_math.h
@@ -40,6 +40,11 @@
#if defined(_MSC_VER)
+/* This is to ensure that we get M_PI, etc. definitions */
+#if !defined(_USE_MATH_DEFINES)
+#error _USE_MATH_DEFINES define required when building with MSVC
+#endif
+
#if _MSC_VER < 1800
#define isfinite(x) _finite((double)(x))
#define isnan(x) _isnan((double)(x))