diff --git a/Source/win32/WIN32Server.m b/Source/win32/WIN32Server.m
index e98c4012..537ecad2 100644
--- a/Source/win32/WIN32Server.m
+++ b/Source/win32/WIN32Server.m
@@ -63,6 +63,18 @@
 
 #include <math.h>
 
+// The Windows SDK declares BOOL as an int.  Objective C defines BOOl as a char.
+// Those two types clash.  MinGW's implementation of the Windows SDK uses the WINBOOL
+// type to avoid this clash.  When compiling natively on Windows, we need to manually
+// define WINBOOL.
+// MinGW will define _DEF_WINBOOL_ if it has defined WINBOOL so we can use the same trick
+// here.
+// See https://github.com/mingw-w64/mingw-w64/blob/master/mingw-w64-headers/include/ntdef.h#L355
+#ifndef _DEF_WINBOOL_
+#define _DEF_WINBOOL_
+typedef int WINBOOL;
+#endif
+
 // To update the cursor..
 static BOOL update_cursor = NO;
 static BOOL should_handle_cursor = NO;
diff --git a/Source/win32/w32_windowdisplay.m b/Source/win32/w32_windowdisplay.m
index 8f61e9e7..5487d1ce 100644
--- a/Source/win32/w32_windowdisplay.m
+++ b/Source/win32/w32_windowdisplay.m
@@ -33,6 +33,18 @@
 #include "win32/WIN32Server.h"
 #include "win32/WIN32Geometry.h"
 
+// The Windows SDK declares BOOL as an int.  Objective C defines BOOl as a char.
+// Those two types clash.  MinGW's implementation of the Windows SDK uses the WINBOOL
+// type to avoid this clash.  When compiling natively on Windows, we need to manually
+// define WINBOOL.
+// MinGW will define _DEF_WINBOOL_ if it has defined WINBOOL so we can use the same trick
+// here.
+// See https://github.com/mingw-w64/mingw-w64/blob/master/mingw-w64-headers/include/ntdef.h#L355
+#ifndef _DEF_WINBOOL_
+#define _DEF_WINBOOL_
+typedef int WINBOOL;
+#endif
+
 static void 
 invalidateWindow(WIN32Server *svr, HWND hwnd, RECT rect)
 {
diff --git a/Tools/win32pbs.m b/Tools/win32pbs.m
index 740dc7c8..a989bba2 100755
--- a/Tools/win32pbs.m
+++ b/Tools/win32pbs.m
@@ -40,6 +40,18 @@
 #include <sys/file.h>
 #endif
 
+// The Windows SDK declares BOOL as an int.  Objective C defines BOOl as a char.
+// Those two types clash.  MinGW's implementation of the Windows SDK uses the WINBOOL
+// type to avoid this clash.  When compiling natively on Windows, we need to manually
+// define WINBOOL.
+// MinGW will define _DEF_WINBOOL_ if it has defined WINBOOL so we can use the same trick
+// here.
+// See https://github.com/mingw-w64/mingw-w64/blob/master/mingw-w64-headers/include/ntdef.h#L355
+#ifndef _DEF_WINBOOL_
+#define _DEF_WINBOOL_
+typedef int WINBOOL;
+#endif
+
 @interface Win32PbOwner : NSObject
 {
   NSPasteboard	*_pb;