diff --git a/crates/async-compression/src/generic/write/buf_writer.rs b/crates/async-compression/src/generic/write/buf_writer.rs
index 22f677e5..8db1797b 100644
--- a/crates/async-compression/src/generic/write/buf_writer.rs
+++ b/crates/async-compression/src/generic/write/buf_writer.rs
@@ -136,7 +136,13 @@ impl BufWriter {
     ) -> Poll<io::Result<&mut [u8]>> {
         ready!(self.partial_flush_buf(poll_write))?;
 
-        if self.written > 0 {
+        // when the flushed data is larger than or equal to half of yet-to-be-flushed data,
+        // the copyback could use version of memcpy that do copies from the head of the buffer.
+        // Anything smaller than that, an overlap would happen that forces use of memmove.
+        if self.written >= (self.buffered / 3)
+            || self.written >= 512
+            || self.buffered == self.buf.len()
+        {
             self.remove_written();
         }