diff --git a/mlir/lib/Dialect/Math/Transforms/PolynomialApproximation.cpp b/mlir/lib/Dialect/Math/Transforms/PolynomialApproximation.cpp
--- a/mlir/lib/Dialect/Math/Transforms/PolynomialApproximation.cpp
+++ b/mlir/lib/Dialect/Math/Transforms/PolynomialApproximation.cpp
@@ -441,6 +441,9 @@
   ans0 = builder.create<math::FmaOp>(ans0, x, x);
 
   // Correct for the input mapping's angles:
+#ifdef _WIN32
+#define _USE_MATH_DEFINES
+#endif
   Value mpi4 = bcast(f32Cst(builder, M_PI_4));
   Value ans2 = builder.create<arith::AddFOp>(mpi4, ans0);
   Value ans = builder.create<arith::SelectOp>(cmp2, ans2, ans0);