diff --git a/include/libxml/xmlstring.h b/include/libxml/xmlstring.h
index 1dfc5ea0..0bc68888 100644
--- a/include/libxml/xmlstring.h
+++ b/include/libxml/xmlstring.h
@@ -59,7 +59,7 @@ XMLPUBFUN const xmlChar * XMLCALL
                                          const xmlChar *val);
 XMLPUBFUN const xmlChar * XMLCALL
                 xmlStrcasestr            (const xmlChar *str,
-                                         xmlChar *val);
+                                         const xmlChar *val);
 XMLPUBFUN int XMLCALL
                 xmlStrcmp                (const xmlChar *str1,
                                          const xmlChar *str2);
diff --git a/xmlstring.c b/xmlstring.c
index 4f3b3739..910f2444 100644
--- a/xmlstring.c
+++ b/xmlstring.c
@@ -366,7 +366,7 @@ xmlStrstr(const xmlChar *str, const xmlChar *val) {
  */
 
 const xmlChar *
-xmlStrcasestr(const xmlChar *str, xmlChar *val) {
+xmlStrcasestr(const xmlChar *str, const xmlChar *val) {
     int n;
     
     if (str == NULL) return(NULL);