--- a/src/http/modules/ngx_http_realip_module.c
+++ b/src/http/modules/ngx_http_realip_module.c
@@ -188,6 +188,7 @@ ngx_http_realip_from(ngx_conf_t *cf, ngx
 {
     ngx_http_realip_loc_conf_t *rlcf = conf;
 
+    ngx_int_t                 rc;
     ngx_str_t                *value;
     ngx_inet_cidr_t           in_cidr;
     ngx_http_realip_from_t   *from;
@@ -215,12 +216,19 @@ ngx_http_realip_from(ngx_conf_t *cf, ngx
         return NGX_CONF_OK;
     }
 
-    if (ngx_ptocidr(&value[1], &in_cidr) == NGX_ERROR) {
+    rc = ngx_ptocidr(&value[1], &in_cidr);
+
+    if (rc == NGX_ERROR) {
         ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "invalid parameter \"%V\"",
                            &value[1]);
         return NGX_CONF_ERROR;
     }
 
+    if (rc == NGX_DONE) {
+        ngx_conf_log_error(NGX_LOG_WARN, cf, 0,
+                           "low address bits of %V are meaningless", &value[1]);
+    }
+
     from->mask = in_cidr.mask;
     from->addr = in_cidr.addr;