diff --git a/src/falco.cpp b/src/falco.cpp
index a94d478..87424fb 100644
--- a/src/falco.cpp
+++ b/src/falco.cpp
@@ -536,7 +536,8 @@ main(int argc, char *argv[]) {
     // restrict buffer size to avoid using a possibly harmful amount of memory
     const auto get_sz = [](const auto &i) { return i.size; };
     const auto max_sz = std::ranges::max(std::views::transform(infos, get_sz));
-    buffer_size = buffer_size < max_sz ? buffer_size : min_buf_size;
+    buffer_size =
+      buffer_size < max_sz ? buffer_size : std::max(max_sz, min_buf_size);
 
     const auto min_buffer_size = get_min_buffer_size(max_read_length);
     if (std::cmp_greater(min_buffer_size, buffer_size)) {
diff --git a/src/fastq_bgzf_file.cpp b/src/fastq_bgzf_file.cpp
index 91d30a7..719e928 100644
--- a/src/fastq_bgzf_file.cpp
+++ b/src/fastq_bgzf_file.cpp
@@ -144,8 +144,8 @@ fastq_bgzf_file::get_chunks(std::int64_t n_chunks,
   const auto n_bytes_available = output_last;
   n_chunks = std::min((n_bytes_available + min_chunk_size - 1) / min_chunk_size,
                       n_chunks);
-  const auto [chunk_size, remainder] = std::div(n_bytes_available, n_chunks);
-  assert(n_chunks > 0);
+  const auto [chunk_size, remainder] = std::div(
+    n_bytes_available, std::max(static_cast<std::int64_t>(1), n_chunks));
   std::int64_t start_pos{};
   std::int64_t chunk_end{};
   for (const auto chunk_idx : std::views::iota(0, n_chunks)) {