diff --git a/parser.c b/parser.c
index a22eb4e..8d34e72 100644
--- a/parser.c
+++ b/parser.c
@@ -1271,7 +1271,7 @@
  */
 
 const xmlChar *
-xmlStrstr(const xmlChar *str, xmlChar *val) {
+xmlStrstr(const xmlChar *str, const xmlChar *val) {
     int n;
     
     if (str == NULL) return(NULL);