diff --git a/src/main.c b/src/main.c
index f586f26..97f9c9c 100644
--- a/src/main.c
+++ b/src/main.c
@@ -60,7 +60,7 @@ void print_lines(const char *first, ...)
 	va_end(args);
 }
 
-static inline int parse_extras_token(manifest_t *conf, char *s)
+static inline int parse_extras_token(manifest_t *conf, const char *s)
 {
 	if (!strcmp(s, "list")) {
 		print_lines("nob", "Cleanup", "format", NULL);
diff --git a/src/util.c b/src/util.c
index e8096f8..bde74db 100644
--- a/src/util.c
+++ b/src/util.c
@@ -31,7 +31,7 @@ licence_t TOlicence(char *src)
 	return UNL;
 }
 
-char *str_dup(char *s)
+char *str_dup(const char *s)
 {
 	char *new = malloc(strlen(s) + 1);
 	if (!new)
@@ -40,7 +40,7 @@ char *str_dup(char *s)
 	return new;
 }
 
-char *tostrupr(char *s)
+char *tostrupr(const char *s)
 {
 	char *new = malloc(strlen(s) + 1);
 	if (!new)
diff --git a/src/util.h b/src/util.h
index e78f4be..74ecfeb 100644
--- a/src/util.h
+++ b/src/util.h
@@ -16,8 +16,8 @@ licence_t TOlicence(char *s);
 int getopt_long(int argc, char *const argv[], const char *optstring,
 		const struct option *longopts, int *longindex);
 
-char *str_dup(char *s);
-char *tostrupr(char *s);
+char *str_dup(const char *s);
+char *tostrupr(const char *s);
 
 extern int fno;
 extern bool flast;