diff --git a/src/include/curses.h b/src/include/curses.h
index 04060fe2..1f6fe029 100644
--- a/src/include/curses.h
+++ b/src/include/curses.h
@@ -443,7 +443,8 @@ extern int wborder ( WINDOW *, chtype, chtype, chtype, chtype, chtype, chtype,
 extern int wclrtobot ( WINDOW * ) __nonnull;
 extern int wclrtoeol ( WINDOW * ) __nonnull;
 extern void wcursyncup ( WINDOW * );
-extern int wcolour_set ( WINDOW *, short, void * ) __nonnull;
+extern int wcolour_set ( WINDOW *, short, void * )
+	__attribute__ (( nonnull (1)));
 #define wcolor_set(w,s,v) wcolour_set((w),(s),(v))
 extern int wdelch ( WINDOW * ) __nonnull;
 extern int wdeleteln ( WINDOW * ) __nonnull;