diff --git a/toolbox/du.c b/toolbox/du.c
index 06374a4..fc7c943 100644
--- a/toolbox/du.c
+++ b/toolbox/du.c
@@ -62,7 +62,7 @@
 
 int	linkchk(dev_t, ino_t);
 void	prstat(const char *, int64_t);
-void	usage(void);
+static void	usage(void);
 
 long blocksize;
 
@@ -312,7 +312,7 @@
 	return 0;
 }
 
-void
+static void
 usage(void)
 {