diff --git a/lib/bundix/commandline.rb b/lib/bundix/commandline.rb
index da93386..586fda8 100644
--- a/lib/bundix/commandline.rb
+++ b/lib/bundix/commandline.rb
@@ -100,14 +100,14 @@ def handle_magic
       ENV['BUNDLE_GEMFILE'] = options[:gemfile]
 
       if options[:magic]
-        fail unless system(
-          Bundix::NIX_SHELL, '-p', options[:ruby],
-          "bundler.override { ruby = #{options[:ruby]}; }",
-          "--command", "bundle lock --lockfile=#{options[:lockfile]}")
-        fail unless system(
-          Bundix::NIX_SHELL, '-p', options[:ruby],
-          "bundler.override { ruby = #{options[:ruby]}; }",
-          "--command", "bundle pack --all --path #{options[:bundle_pack_path]}")
+        prefix =
+          if ENV['IN_NIX_SHELL']
+            []
+          else
+            [Bundix::NIX_SHELL, '-p', options[:ruby], "bundler.override { ruby = #{options[:ruby]}; }", "--command"]
+          end
+        fail unless system(*prefix, "bundle lock --lockfile=#{options[:lockfile]}")
+        fail unless system(*prefix, "bundle pack --path #{options[:bundle_pack_path]}")
       end
     end
 
diff --git a/lib/bundix/source.rb b/lib/bundix/source.rb
index 17012aa..43577af 100644
--- a/lib/bundix/source.rb
+++ b/lib/bundix/source.rb
@@ -20,7 +20,7 @@ def download(file, url)
       end
 
       begin
-        open(uri.to_s, 'r', 0600, open_options) do |net|
+        URI.open(uri.to_s, 'r', 0600, open_options) do |net|
           File.open(file, 'wb+') { |local|
             File.copy_stream(net, local)
           }