diff --git a/src/libstore/filetransfer.hh b/src/libstore/filetransfer.hh
index d836ab2c4..43a384d71 100644
--- a/src/libstore/filetransfer.hh
+++ b/src/libstore/filetransfer.hh
@@ -50,8 +50,9 @@ struct FileTransferSettings : Config
 
     Setting<size_t> downloadBufferSize{this, 64 * 1024 * 1024, "download-buffer-size",
         R"(
-          The size of Nix's internal download buffer during `curl` transfers. If data is
+          The size of Nix's internal download buffer in bytes during `curl` transfers. If data is
           not processed quickly enough to exceed the size of this buffer, downloads may stall.
+          The default is 67108864 (64 MiB).
         )"};
 };