diff --git a/build.sh b/build.sh
index 2126b4a..260d93b 100644
--- a/build.sh
+++ b/build.sh
@@ -1,4 +1,11 @@
 #!/usr/bin/env bash
+set -e
+
+if ! [ "x$1" = "xdo" ]; then
+    echo "A part of the source code is witheld (game_payload/src/tp6.c) to make abuse more difficult. Please download a binary release"
+    exit
+fi
+shift
 
 strip="x86_64-w64-mingw32-strip"