diff --git a/libtransmission/tr-buffer.h b/libtransmission/tr-buffer.h
index b44ad8f5b..dd0df0d4d 100644
--- a/libtransmission/tr-buffer.h
+++ b/libtransmission/tr-buffer.h
@@ -264,7 +264,22 @@ public:
 
     virtual std::pair<value_type*, size_t> reserve_space(size_t n_bytes) override
     {
-        buf_.resize(end_pos_ + n_bytes);
+        if (auto const free_at_end = buf_.size() - end_pos_; free_at_end < n_bytes)
+        {
+            if (auto const total_free = begin_pos_ + free_at_end; total_free >= n_bytes)
+            {
+                // move data so that all free space is at the end
+                auto const size = this->size();
+                std::copy(data(), data() + size, std::data(buf_));
+                begin_pos_ = 0;
+                end_pos_ = size;
+            }
+            else // even `total_free` is not enough, so resize
+            {
+                buf_.resize(end_pos_ + n_bytes);
+            }
+        }
+
         return { buf_.data() + end_pos_, n_bytes };
     }