serialise: fix buffer size used, hide method for internal use only

Fixes #2169.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
index 35603af7082a..3dd8cec290cb 100644
--- a/src/nix-daemon/nix-daemon.cc
+++ b/src/nix-daemon/nix-daemon.cc
@@ -197,7 +197,8 @@ struct TunnelSource : BufferedSource
 {
     Source & from;
     TunnelSource(Source & from) : from(from) { }
-    size_t readUnbuffered(unsigned char * data, size_t len)
+protected:
+    size_t readUnbuffered(unsigned char * data, size_t len) override
     {
         to << STDERR_READ << len;
         to.flush();