diff --git a/scripts/install_nix.sh b/scripts/install_nix.sh
index ca43c01e8..94226dba5 100755
--- a/scripts/install_nix.sh
+++ b/scripts/install_nix.sh
@@ -1,99 +1,106 @@
 #!/usr/bin/env bash
 
 # Do initial nix install if nix is not available in PATH
 if ! command -v nix > /dev/null; then
   sh <(curl -L https://nixos.org/nix/install) --daemon
 
   # Source nix-daemon.sh to add nix to PATH
   if [[ -e '/nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh' ]]; then
     # Path doesn't exist in shellcheck CI container
     # shellcheck source=/dev/null
     . '/nix/var/nix/profiles/default/etc/profile.d/nix-daemon.sh'
   fi
 fi
 
 # Figure out how many cores the system has, and set cache default
 if [[ "$OSTYPE" == 'darwin'* ]]; then
   NPROC=$(sysctl -n hw.physicalcpu)
   ADMIN_GROUP="@admin"
 elif [[ "$OSTYPE" == 'linux'* ]]; then
   NPROC=$(nproc)
   ADMIN_GROUP="@wheel @sudo"
 fi
 
 # Jobs = The number of different nix packages able to be built at the same time
 # Cores = How many cores an individual job may use. This value is
 #   assigned to $NIX_BUILD_CORES within a nix build environment.
 jobs=$((NPROC / 2)) # Use only half of cores for individual jobs
 cores=4 # Just a good default for consumer hardware
 # NOTE: This has the potential of over-subscribing cores by a factor of 2.
 # Potential load = jobs * cores = (n/2) * 4 = 2n
 # However, this is probably the best compromise as most builds are largely
 # single threaded, with a few exceptions which are massively parrallel.
 
 # Check if nix.conf contains a value, append a default if missing.
 add_if_missing_in_nix_conf() {
   local key="$1"
   local value="$2"
 
   if ! grep "$key" /etc/nix/nix.conf &> /dev/null; then
     echo "/etc/nix/nix.conf is missing a value for ${key}. " \
       "Appending '${key} = ${value}' to /etc/nix/nix.conf"
 
     # Make sure that user can write to file
     if sudo test -w /etc/nix/nix.conf; then
       echo "${key} = ${value}" | sudo tee -a /etc/nix/nix.conf &> /dev/null
     else
       # nix.conf is read only, which is true for NixOS
       echo "Unable to write '${key} = ${value}' to nix.conf, " \
         "please add the value to your nix.conf"
     fi
   fi
 }
 
 # Add value for a given value, append the additional value
 append_value_in_nix_conf() {
   local key="$1"
   local value="$2"
 
   # Add value for key if it's missing entirely
   if ! grep "$key" /etc/nix/nix.conf &> /dev/null; then
     add_if_missing_in_nix_conf "$key" "$value";
     return $?
   fi
 
   # Check that key does not already contain the desired value
   if ! grep "$key" /etc/nix/nix.conf | grep "$value" &> /dev/null; then
     echo "/etc/nix/nix.conf is missing '${value}' for '${key}'. " \
       "Appending '${value}' to '${key}' in /etc/nix/nix.conf"
 
     # Make sure that user can write to file
     if sudo test -w /etc/nix/nix.conf; then
       # Find the line with the related setting, then append the new value
       # Values for nix.conf are space separated
-      sudo sed -i.bak  -e "|$key|s|\$| $value|" /etc/nix/nix.conf
+      sudo sed -i.bak  -e "/$key/s|\$| $value|" /etc/nix/nix.conf
     else
       # nix.conf is read only, which is true for NixOS
       echo "Unable to write to nix.conf, please append '$value' to '$key'" \
         "in your nix.conf"
     fi
   fi
 }
 
 # Check if nix.conf is already configured for a given value.
 add_if_missing_in_nix_conf "trusted-users" "${ADMIN_GROUP} ${USER}"
 add_if_missing_in_nix_conf \
   "experimental-features" "flakes nix-command"
 add_if_missing_in_nix_conf "cores" "${cores}"
 add_if_missing_in_nix_conf "max-jobs" "${jobs}"
+
+# Explictly add default cache for older nix versions to prevent custom cache
+# becoming only trusted cache.
+append_value_in_nix_conf "substituters" "https://cache.nixos.org"
+append_value_in_nix_conf "trusted-public-keys" \
+  "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
+
 append_value_in_nix_conf "substituters" "https://comm.cachix.org"
 append_value_in_nix_conf "trusted-public-keys" \
   "comm.cachix.org-1:70RF31rkmCEhQ9HrXA2uXcpqQKGcUK3TxLJdgcUCaA4="
 
 # Ask user if they would like to use Powerline for bash prompt
 SCRIPT_DIR=$(cd "$(dirname "$0")" || true; pwd -P)
 # Build the nixified script which is aware of Powerline and dependencies
 nix build "$SCRIPT_DIR"'/..#better-prompt'
 # Source file to apply Powerline bootstrap logic
 # shellcheck source=/dev/null
 . "$(nix eval --raw "$SCRIPT_DIR"'/..#better-prompt.outPath')/bin/better-prompt"