diff --git a/scripts/build-deb.sh b/scripts/build-deb.sh
index b1e50f3..23f0f5a 100755
--- a/scripts/build-deb.sh
+++ b/scripts/build-deb.sh
@@ -28,7 +28,7 @@ echo "    VERSION = $VERSION"
 
 echo "==> [4/6] Out-of-tree cmake build"
 BUILD_DIR="$REPO_ROOT/build/deb"
-rm -rf "$BUILD_DIR"
+rm -rf "${BUILD_DIR:?BUILD_DIR must not be empty}"
 mkdir -p "$BUILD_DIR"
 cmake -S "$REPO_ROOT" -B "$BUILD_DIR" -G Ninja -DCMAKE_BUILD_TYPE=Release
 cmake --build "$BUILD_DIR" --parallel