diff --git a/scripts/install-nix-from-closure.sh b/scripts/install-nix-from-closure.sh
index bef5cd4f1..a6966c414 100644
--- a/scripts/install-nix-from-closure.sh
+++ b/scripts/install-nix-from-closure.sh
@@ -1,4 +1,4 @@
-#! /usr/bin/env bash
+#!/bin/sh
 
 set -e
 
@@ -49,7 +49,10 @@ for i in $(cd $self/store >/dev/null && echo *); do
     fi
     if ! [ -e "$dest/store/$i" ]; then
         cp -Rp "$self/store/$i" "$i_tmp"
+        chmod -R a-w "$i_tmp"
+        chmod +w "$i_tmp"
         mv "$i_tmp" "$dest/store/$i"
+        chmod -w "$dest/store/$i"
     fi
 done
 echo "" >&2
@@ -65,6 +68,11 @@ if ! $nix/bin/nix-store --load-db < $self/.reginfo; then
     exit 1
 fi
 
+if ! $nix/bin/nix-store --verify; then
+    echo "$0: store verification failed! Consider deleting /nix and starting over" >&2
+    exit 1
+fi
+
 . $nix/etc/profile.d/nix.sh
 
 if ! $nix/bin/nix-env -i "$nix"; then