diff --git a/Xfuncproto.h.in b/Xfuncproto.h.in
index 303743e..ef9702f 100644
--- a/Xfuncproto.h.in
+++ b/Xfuncproto.h.in
@@ -99,6 +99,7 @@ in this Software without prior written authorization from The Open Group.
 # define _X_EXPORT
 # define _X_HIDDEN
 # define _X_INTERNAL
+# define _X_INLINE
 #endif
 
 #if defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) >= 301)