diff --git a/pkgs/tools/networking/tcpflow/default.nix b/pkgs/tools/networking/tcpflow/default.nix
index 52727f1c49e7..1df0f2c37fc2 100644
--- a/pkgs/tools/networking/tcpflow/default.nix
+++ b/pkgs/tools/networking/tcpflow/default.nix
@@ -36,7 +36,7 @@ stdenv.mkDerivation rec {
   buildInputs = [ openssl zlib libpcap boost automake autoconf ] ++ lib.optional useCairo cairo;
 
   postUnpack = ''
-    pushd tcpflow-*-src/src
+    pushd "$sourceRoot/src"
     cp -rv ${be13_api}/* be13_api/
     cp -rv ${dfxml}/* dfxml/
     cp -rv ${httpparser}/* http-parser/