diff --git a/build/cmake/setup.h.in b/build/cmake/setup.h.in
index 96f61174f5..87e5260d84 100644
--- a/build/cmake/setup.h.in
+++ b/build/cmake/setup.h.in
@@ -83,9 +83,6 @@
 /* NanoX (with wxX11) */
 #cmakedefine01 wxUSE_NANOX
 
-/* MS-DOS with DJGPP */
-#cmakedefine __DOS__ 1
-
 /* Stupid hack; __WINDOWS__ clashes with wx/defs.h */
 #ifndef __WINDOWS__
 #cmakedefine __WINDOWS__ 1
diff --git a/setup.h.in b/setup.h.in
index b8de7c9c50..704c8e8e7d 100644
--- a/setup.h.in
+++ b/setup.h.in
@@ -86,9 +86,6 @@
 /* NanoX (with wxX11) */
 #define wxUSE_NANOX 0
 
-/* MS-DOS with DJGPP */
-#undef __DOS__
-
 /* Stupid hack; __WINDOWS__ clashes with wx/defs.h */
 #ifndef __WINDOWS__
 #undef __WINDOWS__
diff --git a/setup.h_vms b/setup.h_vms
index f5d47d9712..f1517da297 100644
--- a/setup.h_vms
+++ b/setup.h_vms
@@ -127,9 +127,6 @@ typedef pid_t GPid;
 /* NanoX (with wxX11) */
 #define wxUSE_NANOX 0
 
-/* MS-DOS with DJGPP */
-#undef __DOS__
-
 /* Stupid hack; __WINDOWS__ clashes with wx/defs.h */
 #ifndef __WINDOWS__
 #undef __WINDOWS__