diff --git a/os/osdep.h b/os/osdep.h
index 0687f568d..d3c5f4e4f 100644
--- a/os/osdep.h
+++ b/os/osdep.h
@@ -60,6 +60,7 @@ SOFTWARE.
 #include <limits.h>
 #include <stddef.h>
 #include <X11/Xos.h>
+#include <X11/Xmd.h>
 
 /* If EAGAIN and EWOULDBLOCK are distinct errno values, then we check errno
  * for both EAGAIN and EWOULDBLOCK, because some supposedly POSIX