diff --git a/src/include/options.h b/src/include/options.h
index 4555b88..a06fdf4 100644
--- a/src/include/options.h
+++ b/src/include/options.h
@@ -56,7 +56,7 @@ struct opts_s {           /* structure describing run-time options */
 	/*@keep@*/ /*@null@*/ char *format;  /* output format, if any */
 	/*@keep@*/ /*@null@*/ char *pidfile; /* PID file, if any */
 	unsigned int argc;             /* number of non-option arguments */
-	/*@keep@*/ /*@null@*/ char **argv;   /* array of non-option arguments */
+	/*@keep@*/ /*@null@*/ const char **argv;   /* array of non-option arguments */
 	unsigned int argv_length;      /* allocated array size */
 };
 
@@ -65,7 +65,7 @@ struct opts_s {           /* structure describing run-time options */
 
 extern /*@null@*/ /*@only@*/ opts_t opts_parse(unsigned int, char **);
 extern void opts_free(/*@only@*/ opts_t);
-extern bool opts_add_file(opts_t, char *);
+extern bool opts_add_file(opts_t, const char *);
 
 #ifdef __cplusplus
 }
diff --git a/src/main/options.c b/src/main/options.c
index d079cad..53a7494 100644
--- a/src/main/options.c
+++ b/src/main/options.c
@@ -88,7 +88,7 @@ void opts_free( /*@only@ */ opts_t opts)
  * Add a filename to the list of non-option arguments, returning false on
  * error.  The filename is not copied - the pointer is stored.
  */
-bool opts_add_file(opts_t opts, char *filename)
+bool opts_add_file(opts_t opts, const char *filename)
 {
 	/*@-branchstate@ */
 	if ((opts->argc >= opts->argv_length) || (NULL == opts->argv)) {