diff --git a/src/dmap_helpers.c b/src/dmap_helpers.c
index 54ea0905..165c86e0 100644
--- a/src/dmap_helpers.c
+++ b/src/dmap_helpers.c
@@ -153,7 +153,7 @@ dmap_add_literal(struct evbuffer *evbuf, char *tag, char *str, int len)
 }
 
 void
-dmap_add_string(struct evbuffer *evbuf, char *tag, char *str)
+dmap_add_string(struct evbuffer *evbuf, char *tag, const char *str)
 {
   unsigned char buf[4];
   int len;
diff --git a/src/dmap_helpers.h b/src/dmap_helpers.h
index 8575a032..e52ea719 100644
--- a/src/dmap_helpers.h
+++ b/src/dmap_helpers.h
@@ -39,7 +39,7 @@ void
 dmap_add_literal(struct evbuffer *evbuf, char *tag, char *str, int len);
 
 void
-dmap_add_string(struct evbuffer *evbuf, char *tag, char *str);
+dmap_add_string(struct evbuffer *evbuf, char *tag, const char *str);
 
 void
 dmap_send_error(struct evhttp_request *req, char *container, char *errmsg);