diff --git a/include/net.h b/include/net.h
index a29dafc10..dd673f0ec 100644
--- a/include/net.h
+++ b/include/net.h
@@ -526,7 +526,7 @@ extern ushort string_to_VLAN(char *s);
 extern ushort getenv_VLAN(char *);
 
 /* copy a filename (allow for "..." notation, limit length) */
-extern void	copy_filename (char *dst, char *src, int size);
+extern void	copy_filename (char *dst, const char *src, int size);
 
 /* get a random source port */
 extern unsigned int random_port(void);
diff --git a/net/net.c b/net/net.c
index d5a5429d1..7576419b7 100644
--- a/net/net.c
+++ b/net/net.c
@@ -1865,7 +1865,7 @@ NetSetIP(volatile uchar * xip, IPaddr_t dest, int dport, int sport, int len)
 	ip->ip_sum   = ~NetCksum((uchar *)ip, IP_HDR_SIZE_NO_UDP / 2);
 }
 
-void copy_filename (char *dst, char *src, int size)
+void copy_filename (char *dst, const char *src, int size)
 {
 	if (*src && (*src == '"')) {
 		++src;