diff --git a/src/os/unix/ngx_linux_sendfile_chain.c b/src/os/unix/ngx_linux_sendfile_chain.c
index 603f91722..0cedee4e3 100644
--- a/src/os/unix/ngx_linux_sendfile_chain.c
+++ b/src/os/unix/ngx_linux_sendfile_chain.c
@@ -380,6 +380,10 @@ ngx_linux_sendfile_thread(ngx_connection_t *c, ngx_buf_t *file, size_t size)
         return ctx->sent;
     }
 
+    if (task->event.active) {
+        return NGX_DONE;
+    }
+
     ctx->file = file;
     ctx->socket = c->fd;
     ctx->size = size;