diff --git a/include/stringlist.h b/include/stringlist.h
index 2e2addf..e85500a 100644
--- a/include/stringlist.h
+++ b/include/stringlist.h
@@ -8,9 +8,9 @@
 	char *str;
 };
 
-int string_list_add(struct string_list *sl, char *str);
+int string_list_add(struct string_list *sl, const char *str);
 int string_list_add_asprintf(struct string_list *sl, const char *fmt, ...);
-int string_list_add_sorted(struct string_list *sl, char *str);
+int string_list_add_sorted(struct string_list *sl, const char *str);
 int string_list_contains(struct string_list *sl, const char *str);
 void string_list_print_by_column(struct string_list *sl);
 
diff --git a/lib/stringlist.c b/lib/stringlist.c
index 57801b3..8a18366 100644
--- a/lib/stringlist.c
+++ b/lib/stringlist.c
@@ -13,7 +13,7 @@
 	return strcmp(astr, bstr);
 }
 
-int string_list_add(struct string_list *sl, char *str)
+int string_list_add(struct string_list *sl, const char *str)
 {
 	struct string_list *new;
 
@@ -48,7 +48,7 @@
 	return 0;
 }
 
-int string_list_add_sorted(struct string_list *sl, char *str)
+int string_list_add_sorted(struct string_list *sl, const char *str)
 {
 	struct string_list *new;