diff --git a/modules/environment/login/login-inner.nix b/modules/environment/login/login-inner.nix
index cb929ddb..a37b5fd6 100644
--- a/modules/environment/login/login-inner.nix
+++ b/modules/environment/login/login-inner.nix
@@ -6,148 +6,159 @@ let
   inherit (initialPackageInfo) cacert nix;
 
   nixCmd = "${nix}/bin/nix --extra-experimental-features 'flakes nix-command'";
+  isDir = path: builtins.toString path + "/.";
 in
 
-writeText "login-inner" ''
-  # This file is generated by Nix-on-Droid. DO NOT EDIT.
+if ! builtins.pathExists config.user.shell then
+  builtins.abort "config.user.shell does not exist"
+else if isDir config.user.shell then
+  builtins.abort "config.user.shell points to a directory, but it should refer to the shell executable file"
+else
+  writeText "login-inner" ''
+    # This file is generated by Nix-on-Droid. DO NOT EDIT.
 
-  set -eo pipefail
+    set -eo pipefail
 
-  ${lib.optionalString (config.environment.motd != null) ''
-    if [ "$#" -eq 0 ]; then  # if script is called from within Nix-on-Droid app
-      echo "${lib.removeSuffix "\n" config.environment.motd}"
-    fi
-  ''}
-
-  ${lib.optionalString config.build.initialBuild ''
-    if [ -e /etc/UNINTIALISED ]; then
-      export HOME="${config.user.home}"
-      export USER="${config.user.userName}"
-
-      # To prevent gc warnings of nix, see https://github.com/NixOS/nix/issues/3237
-      export GC_NPROCS=1
+    ${lib.optionalString (config.environment.motd != null) ''
+      if [ "$#" -eq 0 ]; then  # if script is called from within Nix-on-Droid app
+        echo "${lib.removeSuffix "\n" config.environment.motd}"
+      fi
+    ''}
 
-      echo "Setting default user profile..."
-      ${nix}/bin/nix-env --switch-profile /nix/var/nix/profiles/per-user/$USER/profile
+    ${lib.optionalString config.build.initialBuild ''
+      if [ -e /etc/UNINTIALISED ]; then
+        export HOME="${config.user.home}"
+        export USER="${config.user.userName}"
 
-      [ "$#" -gt 0 ] || echo "Sourcing Nix environment..."
-      . ${nix}/etc/profile.d/nix.sh
+        # To prevent gc warnings of nix, see https://github.com/NixOS/nix/issues/3237
+        export GC_NPROCS=1
 
-      export NIX_SSL_CERT_FILE=${cacert}
+        echo "Setting default user profile..."
+        ${nix}/bin/nix-env --switch-profile /nix/var/nix/profiles/per-user/$USER/profile
 
-      echo
-      echo "Nix-on-Droid can be set up with channels or with flakes (still experimental)."
-      while [[ -z $USE_FLAKE ]]; do
-        read -r -p "Do you want to set it up with flakes? (y/N) " flakes
+        [ "$#" -gt 0 ] || echo "Sourcing Nix environment..."
+        . ${nix}/etc/profile.d/nix.sh
 
-        if [[ "$flakes" =~ ^[Yy]$ ]]; then
-          USE_FLAKE=1
-        elif [[ "$flakes" =~ ^[Nn]$ || -z "$flakes" ]]; then
-          USE_FLAKE=0
-        else
-          echo "Received invalid input '$flakes', please try again."
-        fi
-      done
+        export NIX_SSL_CERT_FILE=${cacert}
 
-      if [[ "$USE_FLAKE" == 0 ]]; then
-
-        echo "Setting up Nix-on-Droid with channels..."
+        echo
+        echo "Nix-on-Droid can be set up with channels or with flakes (still experimental)."
+        while [[ -z $USE_FLAKE ]]; do
+          read -r -p "Do you want to set it up with flakes? (y/N) " flakes
+
+          if [[ "$flakes" =~ ^[Yy]$ ]]; then
+            USE_FLAKE=1
+          elif [[ "$flakes" =~ ^[Nn]$ || -z "$flakes" ]]; then
+            USE_FLAKE=0
+          else
+            echo "Received invalid input '$flakes', please try again."
+          fi
+        done
 
-        echo "Installing and updating nix-channels..."
-        ${nix}/bin/nix-channel --add ${config.build.channel.nixpkgs} nixpkgs
-        ${nix}/bin/nix-channel --update nixpkgs
-        ${nix}/bin/nix-channel --add ${config.build.channel.nix-on-droid} nix-on-droid
-        ${nix}/bin/nix-channel --update nix-on-droid
+        if [[ "$USE_FLAKE" == 0 ]]; then
 
-        DEFAULT_CONFIG=$(${nix}/bin/nix-instantiate --eval --expr "<nix-on-droid/modules/environment/login/nix-on-droid.nix.default>")
+          echo "Setting up Nix-on-Droid with channels..."
 
-        echo "Installing first Nix-on-Droid generation..."
-        ${nixCmd} build --no-link --file "<nix-on-droid>" nix-on-droid
-        $(${nixCmd} path-info --file "<nix-on-droid>" nix-on-droid)/bin/nix-on-droid switch --file $DEFAULT_CONFIG
+          echo "Installing and updating nix-channels..."
+          ${nix}/bin/nix-channel --add ${config.build.channel.nixpkgs} nixpkgs
+          ${nix}/bin/nix-channel --update nixpkgs
+          ${nix}/bin/nix-channel --add ${config.build.channel.nix-on-droid} nix-on-droid
+          ${nix}/bin/nix-channel --update nix-on-droid
 
-        . "${config.user.home}/.nix-profile/etc/profile.d/nix-on-droid-session-init.sh"
+          DEFAULT_CONFIG=$(${nix}/bin/nix-instantiate --eval --expr "<nix-on-droid/modules/environment/login/nix-on-droid.nix.default>")
 
-        echo "Copying default Nix-on-Droid config..."
-        mkdir --parents $HOME/.config/nixpkgs
-        cp $DEFAULT_CONFIG $HOME/.config/nixpkgs/nix-on-droid.nix
-        chmod u+w $HOME/.config/nixpkgs/nix-on-droid.nix
+          echo "Installing first Nix-on-Droid generation..."
+          ${nixCmd} build --no-link --file "<nix-on-droid>" nix-on-droid
+          $(${nixCmd} path-info --file "<nix-on-droid>" nix-on-droid)/bin/nix-on-droid switch --file $DEFAULT_CONFIG
 
-      else
+          . "${config.user.home}/.nix-profile/etc/profile.d/nix-on-droid-session-init.sh"
 
-        echo "Setting up Nix-on-Droid with flakes..."
+          echo "Copying default Nix-on-Droid config..."
+          mkdir --parents $HOME/.config/nixpkgs
+          cp $DEFAULT_CONFIG $HOME/.config/nixpkgs/nix-on-droid.nix
+          chmod u+w $HOME/.config/nixpkgs/nix-on-droid.nix
 
-        echo "Installing flake from default template..."
-        ${nixCmd} flake new ${config.user.home}/.config/nix-on-droid --template ${config.build.flake.nix-on-droid}
+        else
 
-        ${lib.optionalString config.build.flake.inputOverrides ''
-          echo "Overriding input urls in the flake..."
+          echo "Setting up Nix-on-Droid with flakes..."
+
+          echo "Installing flake from default template..."
+          ${nixCmd} flake new ${config.user.home}/.config/nix-on-droid --template ${config.build.flake.nix-on-droid}
+
+          ${lib.optionalString config.build.flake.inputOverrides ''
+            echo "Overriding input urls in the flake..."
+            while IFS="" read -r p || [[ -n "$p" ]]
+            do
+                if [[ $p =~ (.*)github:NixOS/nixpkgs.*\"\; ]]; then
+                    printf "''${BASH_REMATCH[1]}${config.build.flake.nixpkgs}\";\n" "$p"
+                elif [[ $p =~ (.*)github:nix-community/nix-on-droid.*\"\; ]]; then
+                    printf "''${BASH_REMATCH[1]}${config.build.flake.nix-on-droid}\";\n" "$p"
+                else
+                    printf '%s\n' "$p"
+                fi
+            done <<<$(< "${config.user.home}/.config/nix-on-droid/flake.nix") \
+                      > "${config.user.home}/.config/nix-on-droid/flake.nix"
+          ''}
+
+          echo "Overriding system value in the flake..."
           while IFS="" read -r p || [[ -n "$p" ]]
           do
-              if [[ $p =~ (.*)github:NixOS/nixpkgs.*\"\; ]]; then
-                  printf "''${BASH_REMATCH[1]}${config.build.flake.nixpkgs}\";\n" "$p"
-              elif [[ $p =~ (.*)github:nix-community/nix-on-droid.*\"\; ]]; then
-                  printf "''${BASH_REMATCH[1]}${config.build.flake.nix-on-droid}\";\n" "$p"
-              else
-                  printf '%s\n' "$p"
-              fi
+            if [[ $p =~ (.*)\"aarch64-linux\"(.*) ]]; then
+                printf "''${BASH_REMATCH[1]}\"${targetSystem}\"''${BASH_REMATCH[2]}\n" "$p"
+            else
+                printf '%s\n' "$p"
+            fi
           done <<<$(< "${config.user.home}/.config/nix-on-droid/flake.nix") \
                     > "${config.user.home}/.config/nix-on-droid/flake.nix"
-        ''}
 
-        echo "Overriding system value in the flake..."
-        while IFS="" read -r p || [[ -n "$p" ]]
-        do
-          if [[ $p =~ (.*)\"aarch64-linux\"(.*) ]]; then
-              printf "''${BASH_REMATCH[1]}\"${targetSystem}\"''${BASH_REMATCH[2]}\n" "$p"
-          else
-              printf '%s\n' "$p"
-          fi
-        done <<<$(< "${config.user.home}/.config/nix-on-droid/flake.nix") \
-                  > "${config.user.home}/.config/nix-on-droid/flake.nix"
-
-        echo "Installing first Nix-on-Droid generation..."
-        ${nixCmd} run ${config.build.flake.nix-on-droid} -- switch --flake ${config.user.home}/.config/nix-on-droid
+          echo "Installing first Nix-on-Droid generation..."
+          ${nixCmd} run ${config.build.flake.nix-on-droid} -- switch --flake ${config.user.home}/.config/nix-on-droid
 
-        . "${config.user.home}/.nix-profile/etc/profile.d/nix-on-droid-session-init.sh"
+          . "${config.user.home}/.nix-profile/etc/profile.d/nix-on-droid-session-init.sh"
 
-      fi
-
-      echo
-      echo "Congratulations! Now you have Nix installed with some default packages like bashInteractive, \
-    coreutils, cacert and, most importantly, Nix-on-Droid itself to manage local configuration, see"
-      echo "  nix-on-droid help"
+        fi
 
-      if [[ "$USE_FLAKE" == 0 ]]; then
-        echo "or the config file"
-        echo "  ~/.config/nixpkgs/nix-on-droid.nix"
-        echo
-        echo "You can go for the bare Nix-on-Droid setup or you can configure your phone via home-manager. See \
-    config file for further information."
-        echo
-      else
-        echo "or the flake"
-        echo "  ~/.config/nix-on-droid/"
-        echo
-        echo "You can go for the bare Nix-on-Droid setup or you can configure your phone via home-manager. See \
-    other templates in ${config.build.flake.nix-on-droid}."
         echo
+        echo "Congratulations! Now you have Nix installed with some default packages like bashInteractive, \
+      coreutils, cacert and, most importantly, Nix-on-Droid itself to manage local configuration, see"
+        echo "  nix-on-droid help"
+
+        if [[ "$USE_FLAKE" == 0 ]]; then
+          echo "or the config file"
+          echo "  ~/.config/nixpkgs/nix-on-droid.nix"
+          echo
+          echo "You can go for the bare Nix-on-Droid setup or you can configure your phone via home-manager. See \
+      config file for further information."
+          echo
+        else
+          echo "or the flake"
+          echo "  ~/.config/nix-on-droid/"
+          echo
+          echo "You can go for the bare Nix-on-Droid setup or you can configure your phone via home-manager. See \
+      other templates in ${config.build.flake.nix-on-droid}."
+          echo
+        fi
       fi
+    ''}
+
+    . "${config.user.home}/.nix-profile/etc/profile.d/nix-on-droid-session-init.sh"
+
+    ${lib.optionalString config.build.initialBuild ''
+      exec /usr/bin/env bash  # otherwise it'll be a limited bash that came with Nix
+    ''}
+
+    usershell="${config.user.shell}"
+    if [ "$#" -gt 0 ]; then  # if script is not called from within Nix-on-Droid app
+      exec /usr/bin/env "$@"
+    elif [ -d "$usershell" ]; then
+      echo "Cannot execute shell '${config.user.shell}', it is a directory."
+      echo "Unlike nixos you should point `user.shell` to the exact binary."
+      echo "Falling back to bash"
+      exec -l bash
+    elif [ -x "$usershell" ]; then
+      exec -a "-''${usershell##*/}" "$usershell"
+    else
+      echo "Cannot execute shell '${config.user.shell}', falling back to bash"
+      exec -l bash
     fi
-  ''}
-
-  . "${config.user.home}/.nix-profile/etc/profile.d/nix-on-droid-session-init.sh"
-
-  ${lib.optionalString config.build.initialBuild ''
-    exec /usr/bin/env bash  # otherwise it'll be a limited bash that came with Nix
-  ''}
-
-  usershell="${config.user.shell}"
-  if [ "$#" -gt 0 ]; then  # if script is not called from within Nix-on-Droid app
-    exec /usr/bin/env "$@"
-  elif [ -x "$usershell" ]; then
-    exec -a "-''${usershell##*/}" "$usershell"
-  else
-    echo "Cannot execute shell '${config.user.shell}', falling back to bash"
-    exec -l bash
-  fi
-''
+  ''