diff --git a/src/http/modules/ngx_http_upstream_keepalive_module.c b/src/http/modules/ngx_http_upstream_keepalive_module.c
index d10e3d0..a2ad5aa 100644
--- a/src/http/modules/ngx_http_upstream_keepalive_module.c
+++ b/src/http/modules/ngx_http_upstream_keepalive_module.c
@@ -502,6 +502,10 @@
     kcf = ngx_http_conf_upstream_srv_conf(uscf,
                                           ngx_http_upstream_keepalive_module);
 
+    if (kcf->original_init_upstream) {
+        return "is duplicate";
+    }
+
     kcf->original_init_upstream = uscf->peer.init_upstream
                                   ? uscf->peer.init_upstream
                                   : ngx_http_upstream_init_round_robin;