diff --git a/src-tauri/src/macos.rs b/src-tauri/src/macos.rs
index af1052f8a..4053be31f 100644
--- a/src-tauri/src/macos.rs
+++ b/src-tauri/src/macos.rs
@@ -83,16 +83,23 @@ fn same_group(a: &NSWindow, b: &NSWindow) -> bool {
     }
 }
 
-/// Puts `members` in one native tab group and shows `selected`.
-pub fn sync_tab_group(members: Vec<WebviewWindow>, selected: &WebviewWindow) -> tauri::Result<()> {
+/// Adds `members` to the existing anchor's native tab group and shows `selected`.
+pub fn sync_tab_group(
+    members: Vec<WebviewWindow>,
+    anchor: &WebviewWindow,
+    selected: &WebviewWindow,
+) -> tauri::Result<()> {
+    let anchor = anchor.clone();
     let target = selected.clone();
     on_main(selected, move || {
         let Some(shown) = native(&target) else { return };
-        for member in members.iter().filter(|m| m.label() != target.label()) {
+        let Some(anchor_window) = native(&anchor) else { return };
+        // Joining into a new tab's desktop window would take the existing group out of full screen.
+        for member in members.iter().filter(|m| m.label() != anchor.label()) {
             if let Some(window) = native(member)
-                && !same_group(shown, window)
+                && !same_group(anchor_window, window)
             {
-                shown.addTabbedWindow_ordered(window, objc2_app_kit::NSWindowOrderingMode::Above);
+                anchor_window.addTabbedWindow_ordered(window, objc2_app_kit::NSWindowOrderingMode::Above);
             }
         }
         if let Some(group) = shown.tabGroup() {
diff --git a/src-tauri/src/window_groups.rs b/src-tauri/src/window_groups.rs
index 699a7a00c..85335be40 100644
--- a/src-tauri/src/window_groups.rs
+++ b/src-tauri/src/window_groups.rs
@@ -100,8 +100,9 @@ pub fn select(app: &AppHandle, caller: &str, target: &str) -> IdeResult<()> {
 #[cfg(target_os = "macos")]
 fn native_select(app: &AppHandle, group: &Group, to: &WebviewWindow) -> IdeResult<()> {
     let members = group.members.iter().filter_map(|m| app.get_webview_window(m)).collect();
+    let anchor = app.get_webview_window(&group.selected).unwrap_or_else(|| to.clone());
     to.unminimize().map_err(|e| IdeError::internal(e.to_string()))?;
-    crate::macos::sync_tab_group(members, to).map_err(|e| IdeError::internal(e.to_string()))
+    crate::macos::sync_tab_group(members, &anchor, to).map_err(|e| IdeError::internal(e.to_string()))
 }
 
 #[cfg(target_os = "macos")]