diff --git a/src/http/modules/ngx_http_realip_module.c b/src/http/modules/ngx_http_realip_module.c
index cfaa4c9..fca81eb 100644
--- a/src/http/modules/ngx_http_realip_module.c
+++ b/src/http/modules/ngx_http_realip_module.c
@@ -387,6 +387,10 @@
 
     ngx_str_t  *value;
 
+    if (rlcf->type != NGX_CONF_UNSET_UINT) {
+        return "is duplicate";
+    }
+
     value = cf->args->elts;
 
     if (ngx_strcmp(value[1].data, "X-Real-IP") == 0) {