ngx_strcasecmp()/ngx_strncasecmp()
diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 5286000..79d372c 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -2313,7 +2313,7 @@
 
         while (*++p == ' ') { /* void */ }
 
-        if (ngx_strncasecmp(p, "charset=", 8) != 0) {
+        if (ngx_strncasecmp(p, (u_char *) "charset=", 8) != 0) {
             continue;
         }