diff --git a/nixos/modules/config/shells-environment.nix b/nixos/modules/config/shells-environment.nix
index 9dc4749b08d1..41b1b32768ff 100644
--- a/nixos/modules/config/shells-environment.nix
+++ b/nixos/modules/config/shells-environment.nix
@@ -162,8 +162,17 @@ in
         /bin/sh
       '';
 
+    # For resetting environment with `. /etc/set-environment` when needed
+    # and discoverability (see motivation of #30418).
+    environment.etc."set-environment".source = config.system.build.setEnvironment;
+
     system.build.setEnvironment = pkgs.writeText "set-environment"
        ''
+         # DO NOT EDIT -- this file has been generated automatically.
+
+         # Prevent this file from being sourced by child shells.
+         export __NIXOS_SET_ENVIRONMENT_DONE=1
+
          ${exportedEnvVars}
 
          ${cfg.extraInit}
diff --git a/nixos/modules/programs/bash/bash.nix b/nixos/modules/programs/bash/bash.nix
index 69a1a482d074..e5f5c8d09438 100644
--- a/nixos/modules/programs/bash/bash.nix
+++ b/nixos/modules/programs/bash/bash.nix
@@ -126,7 +126,9 @@ in
     programs.bash = {
 
       shellInit = ''
-        ${config.system.build.setEnvironment.text}
+        if [ -z "$__NIXOS_SET_ENVIRONMENT_DONE" ]; then
+            . ${config.system.build.setEnvironment}
+        fi
 
         ${cfge.shellInit}
       '';
diff --git a/nixos/modules/programs/fish.nix b/nixos/modules/programs/fish.nix
index c8d94a47be28..40b3ff37289f 100644
--- a/nixos/modules/programs/fish.nix
+++ b/nixos/modules/programs/fish.nix
@@ -109,7 +109,9 @@ in
       set fish_function_path ${pkgs.fish-foreign-env}/share/fish-foreign-env/functions $__fish_datadir/functions
       
       # source the NixOS environment config
-      fenv source ${config.system.build.setEnvironment}
+      if [ -z "$__NIXOS_SET_ENVIRONMENT_DONE" ]
+          fenv source ${config.system.build.setEnvironment}
+      end
 
       # clear fish_function_path so that it will be correctly set when we return to $__fish_datadir/config.fish
       set -e fish_function_path
diff --git a/nixos/modules/programs/zsh/zsh.nix b/nixos/modules/programs/zsh/zsh.nix
index 42d4e1d4ada0..c6ab637160d5 100644
--- a/nixos/modules/programs/zsh/zsh.nix
+++ b/nixos/modules/programs/zsh/zsh.nix
@@ -103,7 +103,9 @@ in
         if [ -n "$__ETC_ZSHENV_SOURCED" ]; then return; fi
         export __ETC_ZSHENV_SOURCED=1
 
-        ${config.system.build.setEnvironment.text}
+        if [ -z "$__NIXOS_SET_ENVIRONMENT_DONE" ]; then
+            . ${config.system.build.setEnvironment}
+        fi
 
         ${cfge.shellInit}