diff --git a/repo2docker/buildpacks/nix/__init__.py b/repo2docker/buildpacks/nix/__init__.py
index a4841ebf..4b73cf63 100644
--- a/repo2docker/buildpacks/nix/__init__.py
+++ b/repo2docker/buildpacks/nix/__init__.py
@@ -1,10 +1,10 @@
 """BuildPack for nixpkgs environments"""
 import os
 
-from ..base import BuildPack
+from ..base import BuildPack, BaseImage
 
 
-class NixBuildPack(BuildPack):
+class NixBuildPack(BaseImage):
     """A nix Package Manager BuildPack"""
 
     def get_path(self):
@@ -57,12 +57,14 @@ class NixBuildPack(BuildPack):
             ('${NB_USER}', """
             nix-channel --add https://nixos.org/channels/nixpkgs-unstable nixpkgs && \
             nix-channel --update && \
-            nix-shell default.nix --command "command -v jupyter"
+            nix-shell default.nix
             """)
         ]
 
     def get_start_script(self):
         """The path to a script to be executed as ENTRYPOINT"""
+        # the shell wrapper script duplicates the behaviour of other buildpacks
+        # when it coems to the `start` script
         return "/usr/local/bin/nix-shell-wrapper"
 
     def detect(self):
diff --git a/repo2docker/buildpacks/nix/install-nix.bash b/repo2docker/buildpacks/nix/install-nix.bash
index c4bf70e1..2a9c67f8 100644
--- a/repo2docker/buildpacks/nix/install-nix.bash
+++ b/repo2docker/buildpacks/nix/install-nix.bash
@@ -5,7 +5,7 @@ set -ex
 NIX_VERSION="2.1.1"
 NIX_SHA256="ad10b4da69035a585fe89d7330037c4a5d867a372bb0e52a1542ab95aec67999"
 
-wget https://nixos.org/releases/nix/nix-$NIX_VERSION/nix-$NIX_VERSION-x86_64-linux.tar.bz2
+wget --quiet https://nixos.org/releases/nix/nix-$NIX_VERSION/nix-$NIX_VERSION-x86_64-linux.tar.bz2
 echo "$NIX_SHA256  nix-2.1.1-x86_64-linux.tar.bz2" | sha256sum -c
 tar xjf nix-*-x86_64-linux.tar.bz2
 sh nix-*-x86_64-linux/install
diff --git a/repo2docker/buildpacks/nix/nix-shell-wrapper b/repo2docker/buildpacks/nix/nix-shell-wrapper
index be7a3bfb..1a69e13c 100644
--- a/repo2docker/buildpacks/nix/nix-shell-wrapper
+++ b/repo2docker/buildpacks/nix/nix-shell-wrapper
@@ -8,8 +8,20 @@ _term() {
 
 trap _term SIGTERM
 
-echo "$*"
-nix-shell default.nix --command "$*" &
+echo 'command:' "$@"
+
+# a script in the binder sub-directory take precedence
+if [ -f ./binder/start ]; then
+  chmod u+x ./binder/start
+  nix-shell default.nix --command "./binder/start $@" &
+elif [ -f ./start ]; then
+  chmod u+x ./start
+  nix-shell default.nix --command "./start $@" &
+else
+  nix-shell default.nix --command "$@" &
+fi
 
 PID=$!
+echo 'waiting'
+
 wait "$PID"
diff --git a/tests/nix/binder-dir/README.rst b/tests/nix/binder-dir/README.rst
new file mode 100644
index 00000000..6d79746c
--- /dev/null
+++ b/tests/nix/binder-dir/README.rst
@@ -0,0 +1,4 @@
+default.nix in a binder/ directory
+----------------------------------
+
+Check we find and use `default.nix` when it is in a `binder/` sub-directory.
diff --git a/tests/nix/simple/default.nix b/tests/nix/simple/default.nix
index 7b2f7f59..d417565f 100644
--- a/tests/nix/simple/default.nix
+++ b/tests/nix/simple/default.nix
@@ -11,8 +11,6 @@ in
 pkgs.mkShell {
   buildInputs = with pkgs; [
     python36Packages.numpy
-    python36Packages.scipy
-    python36Packages.jupyterlab
   ];
 
   shellHook = ''
diff --git a/tests/nix/simple/verify b/tests/nix/simple/verify
index 4f794e84..dbd34b2a 100755
--- a/tests/nix/simple/verify
+++ b/tests/nix/simple/verify
@@ -1,3 +1,3 @@
 #!/usr/bin/env python
+
 import numpy
-import scipy
diff --git a/tests/nix/start/README.rst b/tests/nix/start/README.rst
new file mode 100644
index 00000000..e82d782c
--- /dev/null
+++ b/tests/nix/start/README.rst
@@ -0,0 +1,5 @@
+Check `start` works with nix
+----------------------------
+
+In this example we set a environment variable in the `start` script and check
+it works when using the nix build pack.
diff --git a/tests/nix/start/default.nix b/tests/nix/start/default.nix
new file mode 100644
index 00000000..d417565f
--- /dev/null
+++ b/tests/nix/start/default.nix
@@ -0,0 +1,19 @@
+let
+  # Pinning nixpkgs to specific release
+  # To get sha256 use "nix-prefetch-git <url> --rev <commit>"
+  commitRev="5574b6a152b1b3ae5f93ba37c4ffd1981f62bf5a";
+  nixpkgs = builtins.fetchTarball {
+    url = "https://github.com/NixOS/nixpkgs/archive/${commitRev}.tar.gz";
+    sha256 = "1pqdddp4aiz726c7qs1dwyfzixi14shp0mbzi1jhapl9hrajfsjg";
+  };
+  pkgs = import nixpkgs { config = { allowUnfree = true; }; };
+in
+pkgs.mkShell {
+  buildInputs = with pkgs; [
+    python36Packages.numpy
+  ];
+
+  shellHook = ''
+    export NIX_PATH="nixpkgs=${nixpkgs}:."
+  '';
+}
diff --git a/tests/nix/start/start b/tests/nix/start/start
new file mode 100755
index 00000000..c458c91a
--- /dev/null
+++ b/tests/nix/start/start
@@ -0,0 +1,5 @@
+#!/bin/bash
+
+export TEST_START_VAR="var is set"
+
+exec "$@"
diff --git a/tests/nix/start/verify b/tests/nix/start/verify
new file mode 100755
index 00000000..b466ab08
--- /dev/null
+++ b/tests/nix/start/verify
@@ -0,0 +1,9 @@
+#!/bin/bash
+set -euo pipefail
+
+# set value of TEST_START_VAR to empty string when it is not defined
+if [ "${TEST_START_VAR:-}" != "var is set" ]
+then
+  echo "TEST_START_VAR is not set"
+  exit 1
+fi