diff --git a/pkgs/applications/networking/p2p/transgui/default.nix b/pkgs/applications/networking/p2p/transgui/default.nix
index ceccf44819fc..0a2f90ecb711 100644
--- a/pkgs/applications/networking/p2p/transgui/default.nix
+++ b/pkgs/applications/networking/p2p/transgui/default.nix
@@ -29,6 +29,7 @@ stdenv.mkDerivation rec {
   '';
 
   preBuild = ''
+    FPCDIR=${fpc}/lib/fpc/${fpc.version} fpcmake -w
     lazbuild -B transgui.lpr --lazarusdir=${lazarus}/share/lazarus
   '';