diff --git a/modules/environment/session-init.nix b/modules/environment/session-init.nix
index 79f815e..c8f16d0 100644
--- a/modules/environment/session-init.nix
+++ b/modules/environment/session-init.nix
@@ -11,6 +11,12 @@ let
 
   exportAll = vars: concatStringsSep "\n" (mapAttrsToList export vars);
 
+  addToNixPath = nixPathEntry: ''
+    if [[ ":$NIX_PATH:" != *":${nixPathEntry}:"* ]]; then
+      export NIX_PATH="${nixPathEntry}''${NIX_PATH:+:}$NIX_PATH"
+    fi
+  '';
+
   sessionInit = pkgs.writeTextFile {
     name = "nix-on-droid-session-init.sh";
     destination = "/etc/profile.d/nix-on-droid-session-init.sh";
@@ -22,7 +28,9 @@ let
       . $HOME/.nix-profile/etc/profile.d/nix.sh
 
       # workaround for nix 2.4, see https://github.com/NixOS/nixpkgs/issues/149791
-      export NIX_PATH=$HOME/.nix-defexpr/channels''${NIX_PATH:+:}$NIX_PATH
+      ${addToNixPath "${config.user.home}/.nix-defexpr/channels"}
+      # Workaround for https://github.com/NixOS/nix/issues/1865
+      ${addToNixPath "nixpkgs=${config.user.home}/.nix-defexpr/channels/nixpkgs/"}
 
       ${optionalString (config.home-manager.config != null) ''
         if [ -e "$HOME/.nix-profile/etc/profile.d/hm-session-vars.sh" ]; then
@@ -30,9 +38,6 @@ let
         fi
       ''}
 
-      # Workaround for https://github.com/NixOS/nix/issues/1865
-      export NIX_PATH=nixpkgs=$HOME/.nix-defexpr/channels/nixpkgs/:$NIX_PATH
-
       ${exportAll cfg.sessionVariables}
     '';
   };