diff --git a/rope.hpp b/rope.hpp
index 2518023..7a35926 100644
--- a/rope.hpp
+++ b/rope.hpp
@@ -401,7 +401,7 @@ namespace Rope {
         int index        = padded_context_len + 1;
         auto img_ids     = gen_flux_img_ids(h, w, patch_size, bs, axes_dim_num, index);
 
-        int img_pad_len = ((-context_len) % seq_multi_of);
+        int img_pad_len = bound_mod(static_cast<int>(img_ids.size() / bs), seq_multi_of);
         if (img_pad_len > 0) {
             std::vector<std::vector<float>> img_pad_ids(bs * img_pad_len, std::vector<float>(3, 0.f));
             img_ids = concat_ids(img_ids, img_pad_ids, bs);