diff --git a/Eigen/src/Core/arch/Default/Half.h b/Eigen/src/Core/arch/Default/Half.h
index e4c3eefac..95ff9da17 100644
--- a/Eigen/src/Core/arch/Default/Half.h
+++ b/Eigen/src/Core/arch/Default/Half.h
@@ -53,6 +53,7 @@
 // GPU support. Hence the need to disable EIGEN_CONSTEXPR when building
 // Eigen with GPU support
   #pragma push_macro("EIGEN_CONSTEXPR")
+  #undef EIGEN_CONSTEXPR
   #define EIGEN_CONSTEXPR
 #endif