diff --git a/src/os/unix/ngx_files.h b/src/os/unix/ngx_files.h
index 9662621..2efd247 100644
--- a/src/os/unix/ngx_files.h
+++ b/src/os/unix/ngx_files.h
@@ -313,6 +313,8 @@
 ssize_t ngx_file_aio_read(ngx_file_t *file, u_char *buf, size_t size,
     off_t offset, ngx_pool_t *pool);
 
+extern ngx_uint_t  ngx_file_aio;
+
 #endif