diff --git a/setup.h.in b/setup.h.in
index 94bdba822a..e45a71b050 100644
--- a/setup.h.in
+++ b/setup.h.in
@@ -77,12 +77,16 @@
 #undef __OSF__
 #undef __BSD__
 #undef __FREEBSD__
+#undef __DARWIN__
 #undef __NETBSD__
 #undef __VMS__
 #undef __ULTRIX__
 #undef __DATA_GENERAL__
 #undef __EMX__
 
+/* PowerPC Darwin & Mac OS X */
+#undef __POWERPC__
+
 /* Stupid hack; __WINDOWS__ clashes with wx/defs.h */
 #ifndef __WINDOWS__
 #undef __WINDOWS__