diff --git a/include/dwarfs/detail/multi_queue_block_merger_impl.h b/include/dwarfs/detail/multi_queue_block_merger_impl.h
index 3affd2a6..ca0dcf54 100644
--- a/include/dwarfs/detail/multi_queue_block_merger_impl.h
+++ b/include/dwarfs/detail/multi_queue_block_merger_impl.h
@@ -161,7 +161,10 @@ class multi_queue_block_merger_impl : public block_merger_base,
 
     while (active_slots_[ix] && active_slots_[ix].value() != src) {
       ++distance;
-      ix = (ix + 1) % active_slots_.size();
+
+      do {
+        ix = (ix + 1) % active_slots_.size();
+      } while (ix != active_slot_index_ && !active_slots_[ix]);
 
       if (ix == active_slot_index_) {
         auto it = std::find(begin(source_queue_), end(source_queue_), src);