diff --git a/BasiliskII/src/Unix/main_unix.cpp b/BasiliskII/src/Unix/main_unix.cpp
index 4243744b..69b85d9e 100755
--- a/BasiliskII/src/Unix/main_unix.cpp
+++ b/BasiliskII/src/Unix/main_unix.cpp
@@ -63,7 +63,9 @@ struct sigstate {
 # ifdef HAVE_GNOMEUI
 #  include <gnome.h>
 # endif
-# include <X11/Xlib.h>
+# if !defined(GDK_WINDOWING_QUARTZ) && !defined(GDK_WINDOWING_WAYLAND)
+#  include <X11/Xlib.h>
+# endif
 #endif
 
 #ifdef ENABLE_XF86_DGA
@@ -385,7 +387,7 @@ static void usage(const char *prg_name)
 
 int main(int argc, char **argv)
 {
-#ifdef ENABLE_GTK
+#if defined(ENABLE_GTK) && !defined(GDK_WINDOWING_QUARTZ) && !defined(GDK_WINDOWING_WAYLAND)
 	XInitThreads();
 #endif
 	const char *vmdir = NULL;
diff --git a/SheepShaver/src/Unix/main_unix.cpp b/SheepShaver/src/Unix/main_unix.cpp
index ad352607..0c5b76a1 100755
--- a/SheepShaver/src/Unix/main_unix.cpp
+++ b/SheepShaver/src/Unix/main_unix.cpp
@@ -133,8 +133,10 @@
 
 #ifdef ENABLE_GTK
 #include <gtk/gtk.h>
+#if !defined(GDK_WINDOWING_QUARTZ) && !defined(GDK_WINDOWING_WAYLAND)
 #include <X11/Xlib.h>
 #endif
+#endif
 
 #ifdef ENABLE_XF86_DGA
 #include <X11/Xlib.h>
@@ -729,7 +731,7 @@ static bool init_sdl()
 
 int main(int argc, char **argv)
 {
-#ifdef ENABLE_GTK
+#if defined(ENABLE_GTK) && !defined(GDK_WINDOWING_QUARTZ) && !defined(GDK_WINDOWING_WAYLAND)
 	XInitThreads();
 #endif
 	char str[256];