diff --git a/scripts/start_sandbox.sh b/scripts/start_sandbox.sh
index f9b3075a..9be2e47f 100755
--- a/scripts/start_sandbox.sh
+++ b/scripts/start_sandbox.sh
@@ -33,7 +33,7 @@ run_args=(-it --rm)
 run_args+=(-v "$PWD:$WORKDIR")
 
 # mount $TMPDIR as /tmp inside container
-run_args+=(-v "$TMPDIR:/tmp")
+run_args+=(-v "${TMPDIR:-/tmp/}:/tmp")
 
 # name container after image, plus numeric suffix to avoid conflicts
 INDEX=0