diff --git a/include/grpc/support/port_platform.h b/include/grpc/support/port_platform.h
index 27a7b5529f7..9c999b9c811 100644
--- a/include/grpc/support/port_platform.h
+++ b/include/grpc/support/port_platform.h
@@ -126,8 +126,8 @@
 #error Must define exactly one of GPR_ARCH_32, GPR_ARCH_64
 #endif
 
-#if defined(GPR_CPU_LINUX) + defined(GPR_CPU_POSIX) != 1
-#error Must define exactly one of GPR_CPU_LINUX, GPR_CPU_POSIX
+#if defined(GPR_CPU_LINUX) + defined(GPR_CPU_POSIX) + defined(GPR_WIN32) != 1
+#error Must define exactly one of GPR_CPU_LINUX, GPR_CPU_POSIX, GPR_WIN32
 #endif
 
 typedef int16_t gpr_int16;