diff --git a/src/http/ngx_http_header_filter_module.c b/src/http/ngx_http_header_filter_module.c
index 3c3d627c5..63ecfa135 100644
--- a/src/http/ngx_http_header_filter_module.c
+++ b/src/http/ngx_http_header_filter_module.c
@@ -368,11 +368,11 @@ ngx_http_header_filter(ngx_http_request_t *r)
 
     if (r->headers_out.server == NULL) {
         if (clcf->server_tokens) {
-            p = ngx_http_server_full_string;
+            p = (u_char *) ngx_http_server_full_string;
             len = sizeof(ngx_http_server_full_string) - 1;
 
         } else {
-            p = ngx_http_server_string;
+            p = (u_char *) ngx_http_server_string;
             len = sizeof(ngx_http_server_string) - 1;
         }