diff --git a/metacall.rb b/metacall.rb
index a56070a..e3de5cb 100644
--- a/metacall.rb
+++ b/metacall.rb
@@ -142,7 +142,8 @@ def install
     # debug = "set -euxo pipefail\n"
 
     metacall_extra = [
-      "PREFIX=#{prefix}\n",
+      "SCRIPT_DIR=$(cd -- \"$(dirname -- \"${BASH_SOURCE[0]}\" )\" &> /dev/null && pwd)\n",
+      "PREFIX=$(dirname \"${SCRIPT_DIR}\")\n",
       "export LOADER_LIBRARY=\"${PREFIX}/lib\"\n",
       "export SERIAL_LIBRARY_PATH=\"${PREFIX}/lib\"\n",
       "export DETOUR_LIBRARY_PATH=\"${PREFIX}/lib\"\n",