diff --git a/lib/System/Win32/Process.cpp b/lib/System/Win32/Process.cpp
index 3aa6ad4d499..00da74076b0 100644
--- a/lib/System/Win32/Process.cpp
+++ b/lib/System/Win32/Process.cpp
@@ -22,6 +22,11 @@
 //===          and must not be UNIX code
 //===----------------------------------------------------------------------===//
 
+#ifdef __MINGW
+// This ban should be lifted when MinGW 1.0+ has defined this value.
+#  define _HEAPOK (-2)
+#endif
+
 namespace llvm {
 using namespace sys;
 
diff --git a/lib/System/Win32/Process.inc b/lib/System/Win32/Process.inc
index 3aa6ad4d499..00da74076b0 100644
--- a/lib/System/Win32/Process.inc
+++ b/lib/System/Win32/Process.inc
@@ -22,6 +22,11 @@
 //===          and must not be UNIX code
 //===----------------------------------------------------------------------===//
 
+#ifdef __MINGW
+// This ban should be lifted when MinGW 1.0+ has defined this value.
+#  define _HEAPOK (-2)
+#endif
+
 namespace llvm {
 using namespace sys;