diff --git a/lib/slist.c b/lib/slist.c
index 366b247609..88fdd8a2ba 100644
--- a/lib/slist.c
+++ b/lib/slist.c
@@ -58,7 +58,8 @@ static struct curl_slist *slist_get_last(struct curl_slist *list)
  * If an error occurs, NULL is returned and the string argument is NOT
  * released.
  */
-struct curl_slist *Curl_slist_append_nodup(struct curl_slist *list, char *data)
+struct curl_slist *Curl_slist_append_nodup(struct curl_slist *list,
+                                           const char *data)
 {
   struct curl_slist     *last;
   struct curl_slist     *new_item;
@@ -70,7 +71,7 @@ struct curl_slist *Curl_slist_append_nodup(struct curl_slist *list, char *data)
     return NULL;
 
   new_item->next = NULL;
-  new_item->data = data;
+  new_item->data = CURL_UNCONST(data);
 
   /* if this is the first item, then new_item *is* the list */
   if(!list)
diff --git a/lib/slist.h b/lib/slist.h
index 9561fd0226..47a30824db 100644
--- a/lib/slist.h
+++ b/lib/slist.h
@@ -36,6 +36,6 @@ struct curl_slist *Curl_slist_duplicate(struct curl_slist *inlist);
  * it to the list.
  */
 struct curl_slist *Curl_slist_append_nodup(struct curl_slist *list,
-                                           char *data);
+                                           const char *data);
 
 #endif /* HEADER_CURL_SLIST_H */