diff --git a/include/libgen.h b/include/libgen.h
index 5aa3705a0..5825e56ef 100644
--- a/include/libgen.h
+++ b/include/libgen.h
@@ -6,4 +6,5 @@ libgen.h
 
 /* Open Group Base Specifications Issue 6 (not complete) */
 _PROTOTYPE( char *basename, (char *_path)				);
+_PROTOTYPE( char *dirname, (char *_path)				);