diff --git a/src/copy.ml b/src/copy.ml
index b8cbf3438..e002e17a2 100644
--- a/src/copy.ml
+++ b/src/copy.ml
@@ -841,6 +841,14 @@ let transferFileContents
                   fspathTo pathTo fileKind srcFileSize outfd id in
               let eof =
                 Transfer.Rsync.rsyncDecompress blockSize ifd fd showProgress ti
+                  ~copyFn:(fun in_offs len ~fallback ->
+                    (* Flush the buffered output channel just in case since
+                       we manipulate the channel's underlying fd directly. *)
+                    flush fd;
+                    copyFileRange
+                      (Unix.descr_of_in_channel ifd)
+                      (Unix.descr_of_out_channel fd)
+                      in_offs len fallback (fun _ -> ()))
               in
               if eof then close_all infd outfd))
       else
diff --git a/src/transfer.ml b/src/transfer.ml
index 3d7cb4e2e..bed057610 100644
--- a/src/transfer.ml
+++ b/src/transfer.ml
@@ -466,7 +466,7 @@ struct
 
   (* For each transfer instruction, either output a string or copy one or
      several blocks from the old file. *)
-  let rsyncDecompress blockSize infd outfd showProgress (data, pos, len) =
+  let rsyncDecompress blockSize infd outfd ?copyFn showProgress (data, pos, len) =
     let decomprBuf = Bytes.create decomprBufSize in
     let progress = ref 0 in
     let rec copy length =
@@ -478,10 +478,23 @@ struct
         let _ = reallyRead infd decomprBuf 0 length in
         reallyWrite outfd decomprBuf 0 length
     in
+    let copyBlocks' offs length =
+      LargeFile.seek_in infd offs;
+      copy length
+    in
     let copyBlocks n k =
-      LargeFile.seek_in infd (Int64.mul n (Int64.of_int blockSize));
+      let offs = Int64.mul n (Int64.of_int blockSize) in
       let length = k * blockSize in
-      copy length;
+      begin match copyFn with
+      | None -> copyBlocks' offs length
+      | Some f ->
+          let fallback copied =
+            let offs = Int64.add offs (Uutil.Filesize.toInt64 copied)
+            and length = length - (Uutil.Filesize.toInt copied) in
+            copyBlocks' offs length
+          in
+          f (Uutil.Filesize.ofInt64 offs) (Uutil.Filesize.ofInt length) ~fallback;
+      end;
       progress := !progress + length
     in
     let maxPos = pos + len in
diff --git a/src/transfer.mli b/src/transfer.mli
index 121288296..dff54d9eb 100644
--- a/src/transfer.mli
+++ b/src/transfer.mli
@@ -94,6 +94,13 @@ module Rsync :
            int                   (* block size *)
         -> in_channel            (* old file descriptor *)
         -> out_channel           (* output file descriptor *)
+        -> ?copyFn:              (* function for optimized copying *)
+           (   Uutil.Filesize.t  (* input file offset *)
+            -> Uutil.Filesize.t  (* data length *)
+            -> fallback:         (* default function for copying *)
+               (Uutil.Filesize.t (* bytes copied before fallback *)
+                -> unit)
+            -> unit)
         -> (int -> unit)         (* progress report *)
         -> transfer_instruction  (* transfer instruction received *)
         -> bool