diff --git a/src/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
index 5b7f44a..42dd664 100644
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -1240,7 +1240,7 @@
             reserve = len > r->uri.len - alias ? len - (r->uri.len - alias) : 0;
         }
 
-        if (reserve > allocated) {
+        if (reserve > allocated || !allocated) {
 
             /* 16 bytes are preallocation */
             allocated = reserve + 16;