diff --git a/openless-all/app/scripts/macos-capsule-spaces-contract.test.mjs b/openless-all/app/scripts/macos-capsule-spaces-contract.test.mjs
index 0d48305a..f83684b6 100644
--- a/openless-all/app/scripts/macos-capsule-spaces-contract.test.mjs
+++ b/openless-all/app/scripts/macos-capsule-spaces-contract.test.mjs
@@ -26,6 +26,12 @@ assertMatch(
   'macOS capsule should join all Spaces before showing without activation',
 );
 
+assertMatch(
+  macosNoActivateFunction,
+  /FULL_SCREEN_AUXILIARY[\s\S]*?1 << 8[\s\S]*?setCollectionBehavior[\s\S]*?orderFrontRegardless/,
+  'macOS capsule should join fullscreen Spaces as an auxiliary window before showing without activation',
+);
+
 for (const forbidden of ['window.show()', 'set_focus', 'NSApp.activate', 'makeKeyAndOrderFront']) {
   if (executableMacosNoActivateFunction.includes(forbidden)) {
     throw new Error(`macOS capsule no-activate path must not call ${forbidden}`);
diff --git a/openless-all/app/src-tauri/src/coordinator.rs b/openless-all/app/src-tauri/src/coordinator.rs
index b7869133..abb01a28 100644
--- a/openless-all/app/src-tauri/src/coordinator.rs
+++ b/openless-all/app/src-tauri/src/coordinator.rs
@@ -4507,6 +4507,13 @@ fn show_capsule_window_no_activate<R: tauri::Runtime>(
     }
 
     unsafe {
+        const NS_WINDOW_COLLECTION_BEHAVIOR_CAN_JOIN_ALL_SPACES: usize = 1 << 0;
+        const NS_WINDOW_COLLECTION_BEHAVIOR_FULL_SCREEN_AUXILIARY: usize = 1 << 8;
+        let behavior: usize = msg_send![ns_window, collectionBehavior];
+        let behavior = behavior
+            | NS_WINDOW_COLLECTION_BEHAVIOR_CAN_JOIN_ALL_SPACES
+            | NS_WINDOW_COLLECTION_BEHAVIOR_FULL_SCREEN_AUXILIARY;
+        let _: () = msg_send![ns_window, setCollectionBehavior: behavior];
         let _: () = msg_send![ns_window, orderFrontRegardless];
     }
     true