diff --git a/builtins/builtins.c b/builtins/builtins.c
index f1cb35dd..36498e1a 100644
--- a/builtins/builtins.c
+++ b/builtins/builtins.c
@@ -149,7 +149,7 @@ void __do_print(const char *format, const char *types, int width, int mask,
 
 
 int __num_cores() {
-#ifdef _MSC_VER
+#if defined(_MSC_VER) || defined(__MINGW32__)
     // This is quite a hack.  Including all of windows.h to get this definition
     // pulls in a bunch of stuff that leads to undefined symbols at link time.
     // So we don't #include <windows.h> but instead have the equivalent declarations