diff --git a/mlx/backend/cpu/unary.cpp b/mlx/backend/cpu/unary.cpp
index 89d1cafb3..eafe98866 100644
--- a/mlx/backend/cpu/unary.cpp
+++ b/mlx/backend/cpu/unary.cpp
@@ -1,5 +1,8 @@
 // Copyright © 2024 Apple Inc.
 
+// Required for using M_LN2 in MSVC.
+#define _USE_MATH_DEFINES
+
 #include <cassert>
 
 #include "mlx/backend/cpu/unary.h"