diff --git a/usr.bin/csup/rcsfile.c b/usr.bin/csup/rcsfile.c
index 1f3ede154cf2..33caa03e7cf0 100644
--- a/usr.bin/csup/rcsfile.c
+++ b/usr.bin/csup/rcsfile.c
@@ -175,7 +175,8 @@ print_stream(struct stream *s)
  * Parse rcsfile from path and return a pointer to it.
  */
 struct rcsfile *
-rcsfile_frompath(char *path, char *name, char *cvsroot, char *colltag, int ro)
+rcsfile_frompath(const char *path, const char *name, const char *cvsroot,
+    const char *colltag, int ro)
 {
 	struct rcsfile *rf;
 	FILE *infp;
diff --git a/usr.bin/csup/rcsfile.h b/usr.bin/csup/rcsfile.h
index 5fa9f31cb1a5..096ac96e0478 100644
--- a/usr.bin/csup/rcsfile.h
+++ b/usr.bin/csup/rcsfile.h
@@ -42,7 +42,8 @@ struct delta;
 struct stream;
 
 /* Fetching, sending and writing an RCS file. */
-struct rcsfile	*rcsfile_frompath(char *, char *, char *, char *, int);
+struct rcsfile	*rcsfile_frompath(const char *, const char *, const char *,
+		    const char *, int);
 int		 rcsfile_send_details(struct rcsfile *, struct stream *);
 int		 rcsfile_write(struct rcsfile *, struct stream *);
 void		 rcsfile_print(struct rcsfile *);