diff --git a/pkgs/applications/emulators/dynamips/default.nix b/pkgs/applications/emulators/dynamips/default.nix
index a1316a85ab4b..2c529af3a80f 100644
--- a/pkgs/applications/emulators/dynamips/default.nix
+++ b/pkgs/applications/emulators/dynamips/default.nix
@@ -35,6 +35,7 @@ stdenv.mkDerivation rec {
       routers.
     '';
     license = licenses.gpl2Plus;
+    mainProgram = "dynamips";
     maintainers = with maintainers; [ primeos ];
     platforms = platforms.linux ++ platforms.darwin;
   };