diff --git a/modules/system/defaults/NSGlobalDomain.nix b/modules/system/defaults/NSGlobalDomain.nix
index 0224b70..c9633c3 100644
--- a/modules/system/defaults/NSGlobalDomain.nix
+++ b/modules/system/defaults/NSGlobalDomain.nix
@@ -152,6 +152,14 @@ in {
       '';
     };
 
+    system.defaults.NSGlobalDomain.AppleWindowTabbingMode = mkOption {
+      type = types.nullOr types.str;
+      default = null;
+      description = ''
+        Sets the window tabbing when opening a new document: 'manual', 'always', or 'fullscreen'.  The default is 'fullscreen'.
+      '';
+    };
+
     system.defaults.NSGlobalDomain.NSNavPanelExpandedStateForSaveMode = mkOption {
       type = types.nullOr types.bool;
       default = null;
diff --git a/tests/system-defaults-write.nix b/tests/system-defaults-write.nix
index 1c21ca8..06268d0 100644
--- a/tests/system-defaults-write.nix
+++ b/tests/system-defaults-write.nix
@@ -18,6 +18,7 @@
   system.defaults.NSGlobalDomain.NSAutomaticWindowAnimationsEnabled = false;
   system.defaults.NSGlobalDomain.NSDisableAutomaticTermination = true;
   system.defaults.NSGlobalDomain.NSDocumentSaveNewDocumentsToCloud = false;
+  system.defaults.NSGlobalDomain.AppleWindowTabbingMode = "always";
   system.defaults.NSGlobalDomain.NSNavPanelExpandedStateForSaveMode = true;
   system.defaults.NSGlobalDomain.NSNavPanelExpandedStateForSaveMode2 = true;
   system.defaults.NSGlobalDomain.NSTableViewDefaultSizeMode = 2;
@@ -86,6 +87,7 @@
     grep "defaults write -g 'NSAutomaticWindowAnimationsEnabled' -bool NO" ${config.out}/activate-user
     grep "defaults write -g 'NSDisableAutomaticTermination' -bool YES" ${config.out}/activate-user
     grep "defaults write -g 'NSDocumentSaveNewDocumentsToCloud' -bool NO" ${config.out}/activate-user
+    grep "defaults write -g 'AppleWindowTabbingMode' -string 'always'" ${config.out}/activate-user
     grep "defaults write -g 'NSNavPanelExpandedStateForSaveMode' -bool YES" ${config.out}/activate-user
     grep "defaults write -g 'NSNavPanelExpandedStateForSaveMode2' -bool YES" ${config.out}/activate-user
     grep "defaults write -g 'NSTableViewDefaultSizeMode' -int 2" ${config.out}/activate-user