diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 7d18154..3c4d041 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -52,3 +52,20 @@ jobs:
         nix_path: nixpkgs=channel:nixos-20.03
     - run: test $NIX_PATH == "nixpkgs=channel:nixos-20.03"
     - run: nix-build test.nix
+
+  extra-nix-config:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+    - uses: actions/checkout@v2
+    - run: yarn install --frozen-lockfile
+    - run: yarn build
+    - name: Install Nix
+      uses: ./
+      with:
+        extra_nix_config: |
+          sandbox = relaxed
+    - run: cat /etc/nix/nix.conf
+    - run: nix-build test.nix --arg noChroot true
diff --git a/README.md b/README.md
index da8b4de..3c15c7a 100644
--- a/README.md
+++ b/README.md
@@ -35,6 +35,7 @@ with developers.
 - `nix_path`: set `NIX_PATH` environment variable (if set `skip_adding_nixpkgs_channel` will be implicitly enabled)
 
 - `skip_adding_nixpkgs_channel`: set to `true` to skip adding nixpkgs-unstable channel (and save ~5s for each job build)
+- `extra_nix_config`: gets appended to `/etc/nix/nix.conf` if passed.
 
 ---
 
diff --git a/action.yml b/action.yml
index aac769c..c5124a7 100644
--- a/action.yml
+++ b/action.yml
@@ -8,6 +8,8 @@ inputs:
     description: 'Set NIX_PATH environment variable. If set "skip_adding_nixpkgs_channel" will be implicitly enabled'
   skip_adding_nixpkgs_channel:
     description: 'Skip adding nixpkgs-unstable channel'
+  extra_nix_config:
+    description: 'gets appended to `/etc/nix/nix.conf` if passed.'
 branding:
   color: 'blue'
   icon: 'sun'
diff --git a/lib/install-nix.sh b/lib/install-nix.sh
index 01f65df..01b5fe4 100755
--- a/lib/install-nix.sh
+++ b/lib/install-nix.sh
@@ -1,20 +1,35 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
+# Configure Nix
+add_config() {
+  echo "$1" | sudo tee -a /tmp/nix.conf >/dev/null
+}
 # Set jobs to number of cores
-sudo sh -c 'echo max-jobs = auto >> /tmp/nix.conf'
+add_config "max-jobs = auto"
 # Allow binary caches for runner user
-sudo sh -c 'echo trusted-users = root runner >> /tmp/nix.conf'
+add_config "trusted-users = root runner"
+# Append extra nix configuration if provided
+if [[ $INPUT_EXTRA_NIX_CONFIG != "" ]]; then
+  add_config "$INPUT_EXTRA_NIX_CONFIG"
+fi
+
+# Nix installer flags
+installer_options=(
+  --daemon
+  --daemon-user-count 4
+  --darwin-use-unencrypted-nix-store-volume
+  --nix-extra-conf-file /tmp/nix.conf
+)
 
 if [[ $INPUT_SKIP_ADDING_NIXPKGS_CHANNEL = "true" || $INPUT_NIX_PATH != "" ]]; then
-  extra_cmd=--no-channel-add
+  installer_options+=(--no-channel-add)
 else
-  extra_cmd=
   INPUT_NIX_PATH="/nix/var/nix/profiles/per-user/root/channels"
 fi
 
-sh <(curl --retry 5 --retry-connrefused -L ${INPUT_INSTALL_URL:-https://nixos.org/nix/install}) \
-  --daemon --daemon-user-count 4 --nix-extra-conf-file /tmp/nix.conf --darwin-use-unencrypted-nix-store-volume $extra_cmd
+sh <(curl --retry 5 --retry-connrefused -L "${INPUT_INSTALL_URL:-https://nixos.org/nix/install}") \
+  "${installer_options[@]}"
 
 if [[ $OSTYPE =~ darwin ]]; then
   # Disable spotlight indexing of /nix to speed up performance
diff --git a/test.nix b/test.nix
index f95abdf..4f6ba38 100644
--- a/test.nix
+++ b/test.nix
@@ -2,14 +2,17 @@
 { size ? 1 # MB
 , num ? 10 # count 
 , currentTime ? builtins.currentTime
+, noChroot ? false
 }:
 
 with import <nixpkgs> {};
 
 let
-  drv = i: runCommand "${toString currentTime}-${toString i}" {} ''
+  drv = i: runCommand "${toString currentTime}-${toString i}" {
+    __noChroot = noChroot;
+  } ''
     dd if=/dev/zero of=$out bs=${toString size}MB count=1
   '';
 in writeText "empty-${toString num}-${toString size}MB" ''
   ${lib.concatMapStringsSep "" drv (lib.range 1 num)}
-''
\ No newline at end of file
+''