diff --git a/CHANGELOG b/CHANGELOG
index 3caea31..18b6e6b 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,4 +1,4 @@
-2020-12-18
+2020-12-30
 - Added `homebrew` module, to manage formulas installed by Homebrew via `brew bundle`.
 
 2020-10-25
diff --git a/modules/homebrew.nix b/modules/homebrew.nix
index ac89cf6..5088f3c 100644
--- a/modules/homebrew.nix
+++ b/modules/homebrew.nix
@@ -38,13 +38,6 @@ in
       configuring your Brewfile, and installing/updating the formulas therein via
       the <command>brew bundle</command> command, using <command>nix-darwin</command>.
 
-      When enabled, the <literal>HOMEBREW_BUNDLE_FILE</literal> and
-      <literal>HOMEBREW_BUNDLE_NO_LOCK</literal> environment variables are added to
-      <option>environment.variables</option>, so that when if/when you run
-      <command>brew bundle</command> yourself, it will reference the Brewfile generated by this
-      module in the store by default, and skip generating a lockfile (which would fail, since
-      lockfiles are generated in the same directory as the Brewfile).
-
       Note that enabling this option does not install Homebrew. See the Homebrew website for
       installation instructions: https://brew.sh
     '';
@@ -87,6 +80,34 @@ in
       '';
     };
 
+    global.brewfile = mkOption {
+       type = types.bool;
+       default = false;
+       description = ''
+         When enabled, when you manually invoke <command>brew bundle</command>, it will
+         automatically use the Brewfile in the Nix store that this module generates.
+
+         Sets the <literal>HOMEBREW_BUNDLE_FILE</literal> environment variable to the path of the
+         Brewfile in the Nix store that this module generates, by adding it to
+         <option>environment.variables</option>.
+       '';
+     };
+
+     global.noLock = mkOption {
+       type = types.bool;
+       default = false;
+       description = ''
+         When enabled, lockfiles aren't generated when you manually invoke
+         <command>brew bundle [install]</command>. This is often desirable when
+         <option>homebrew.global.brewfile</option> is enabled, since
+         <command>brew bundle [install]</command> will try to write the lockfile in the Nix store,
+         and complain that it can't (though the command will run successfully regardless).
+
+         Sets the <literal>HOMEBREW_BUNDLE_NO_LOCK</literal> environment variable, by adding it to
+         <option>environment.variables</option>.
+       '';
+     };
+
     taps = mkOption {
       type = with types; listOf str;
       default = [];
@@ -175,10 +196,10 @@ in
       optional (cfg.masApps != {}) "mas" ++
       optional (cfg.whalebrews != []) "whalebrew";
 
-    environment.variables = mkIf cfg.enable {
-      HOMEBREW_BUNDLE_FILE = "${brewfile}";
-      HOMEBREW_BUNDLE_NO_LOCK = "1";
-    };
+    environment.variables = mkIf cfg.enable (
+       optionalAttrs cfg.global.brewfile { HOMEBREW_BUNDLE_FILE = "${brewfile}"; } //
+       optionalAttrs cfg.global.noLock { HOMEBREW_BUNDLE_NO_LOCK = "1"; }
+     );
 
     system.activationScripts.homebrew.text = mkIf cfg.enable ''
       # Homebrew Bundle