diff --git a/src/std/c_string.c b/src/std/c_string.c
index 2c80a04da0..89d9a099a5 100644
--- a/src/std/c_string.c
+++ b/src/std/c_string.c
@@ -88,7 +88,7 @@ c_strlist_t *c_strlist_expand(c_strlist_t *strlist, size_t size) {
   return strlist;
 }
 
-int c_strlist_add(c_strlist_t *strlist, char *string) {
+int c_strlist_add(c_strlist_t *strlist, const char *string) {
   if (strlist == NULL || string == NULL) {
     return -1;
   }
diff --git a/src/std/c_string.h b/src/std/c_string.h
index c02968e3e2..93b9bd3289 100644
--- a/src/std/c_string.h
+++ b/src/std/c_string.h
@@ -94,7 +94,7 @@ c_strlist_t *c_strlist_expand(c_strlist_t *strlist, size_t size);
  *
  * @return  0 on success, less than 0 if an error occured.
  */
-int c_strlist_add(c_strlist_t *strlist, char *string);
+int c_strlist_add(c_strlist_t *strlist, const char *string);
 
 /**
  * @brief Destroy the memory of the stringlist.