diff --git a/src/http/modules/ngx_http_image_filter_module.c b/src/http/modules/ngx_http_image_filter_module.c
index c983b973b..bd7a30970 100644
--- a/src/http/modules/ngx_http_image_filter_module.c
+++ b/src/http/modules/ngx_http_image_filter_module.c
@@ -1012,6 +1012,7 @@ transparent:
     b->last_buf = 1;
 
     ngx_http_image_length(r, b);
+    ngx_http_weak_etag(r);
 
     return b;
 }