diff --git a/CHANGELOG.md b/CHANGELOG.md
index c25dfc0..23324e6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,7 @@ The format is based on Keep a Changelog, and this project currently tracks chang
 - Memory search matches against body content in addition to metadata, with metadata weighted higher for relevance.
 - Memory search tokenizer handles Han characters for multilingual queries.
 - Fixed duplicate response in React TUI caused by double Enter key submission in the input handler.
+- Fixed concurrent permission modals overwriting each other in TUI default mode when the LLM returns multiple tool calls in one response; `_ask_permission` now serialises callers via an `asyncio.Lock` so each modal is shown and resolved before the next one is emitted.
 
 ### Changed
 
diff --git a/src/openharness/ui/backend_host.py b/src/openharness/ui/backend_host.py
index fba5a3d..f9bac2a 100644
--- a/src/openharness/ui/backend_host.py
+++ b/src/openharness/ui/backend_host.py
@@ -65,6 +65,7 @@ class ReactBackendHost:
         self._request_queue: asyncio.Queue[FrontendRequest] = asyncio.Queue()
         self._permission_requests: dict[str, asyncio.Future[bool]] = {}
         self._question_requests: dict[str, asyncio.Future[str]] = {}
+        self._permission_lock = asyncio.Lock()
         self._busy = False
         self._running = True
         # Track last tool input per name for rich event emission
@@ -647,27 +648,28 @@ class ReactBackendHost:
         return options
 
     async def _ask_permission(self, tool_name: str, reason: str) -> bool:
-        request_id = uuid4().hex
-        future: asyncio.Future[bool] = asyncio.get_running_loop().create_future()
-        self._permission_requests[request_id] = future
-        await self._emit(
-            BackendEvent(
-                type="modal_request",
-                modal={
-                    "kind": "permission",
-                    "request_id": request_id,
-                    "tool_name": tool_name,
-                    "reason": reason,
-                },
+        async with self._permission_lock:
+            request_id = uuid4().hex
+            future: asyncio.Future[bool] = asyncio.get_running_loop().create_future()
+            self._permission_requests[request_id] = future
+            await self._emit(
+                BackendEvent(
+                    type="modal_request",
+                    modal={
+                        "kind": "permission",
+                        "request_id": request_id,
+                        "tool_name": tool_name,
+                        "reason": reason,
+                    },
+                )
             )
-        )
-        try:
-            return await asyncio.wait_for(future, timeout=300)
-        except asyncio.TimeoutError:
-            log.warning("Permission request %s timed out after 300s, denying", request_id)
-            return False
-        finally:
-            self._permission_requests.pop(request_id, None)
+            try:
+                return await asyncio.wait_for(future, timeout=300)
+            except asyncio.TimeoutError:
+                log.warning("Permission request %s timed out after 300s, denying", request_id)
+                return False
+            finally:
+                self._permission_requests.pop(request_id, None)
 
     async def _ask_question(self, question: str) -> str:
         request_id = uuid4().hex
diff --git a/tests/test_ui/test_react_backend.py b/tests/test_ui/test_react_backend.py
index 964c1df..908b06a 100644
--- a/tests/test_ui/test_react_backend.py
+++ b/tests/test_ui/test_react_backend.py
@@ -406,3 +406,51 @@ async def test_backend_host_apply_provider_select_command_shows_single_segment_t
     assert should_continue is True
     user_event = next(item for item in events if item.type == "transcript_item" and item.item and item.item.role == "user")
     assert user_event.item.text == "/provider"
+
+
+@pytest.mark.asyncio
+async def test_concurrent_ask_permission_are_serialised():
+    """Concurrent _ask_permission calls must be serialised so the frontend
+    never receives two overlapping modal_request events.
+
+    Without _permission_lock the second call emits a modal_request before the
+    first future is resolved, overwriting the frontend's modal state. The first
+    tool then silently waits 300 s and gets Permission denied.
+    """
+    host = ReactBackendHost(BackendHostConfig(api_client=StaticApiClient("unused")))
+
+    emitted_order: list[str] = []
+
+    async def _fake_emit(event: BackendEvent) -> None:
+        if event.type == "modal_request" and event.modal:
+            emitted_order.append(str(event.modal.get("request_id", "")))
+
+    host._emit = _fake_emit  # type: ignore[method-assign]
+
+    async def _ask_and_approve(tool: str) -> bool:
+        # Start the ask; a background task resolves the future once it appears.
+        async def _resolver():
+            # Busy-wait until this tool's future is registered.
+            while True:
+                await asyncio.sleep(0)
+                for rid, fut in list(host._permission_requests.items()):
+                    if not fut.done():
+                        fut.set_result(True)
+                        return
+
+        asyncio.create_task(_resolver())
+        return await host._ask_permission(tool, "reason")
+
+    # Fire two permission requests concurrently.
+    result_a, result_b = await asyncio.gather(
+        _ask_and_approve("write_file"),
+        _ask_and_approve("bash"),
+    )
+
+    assert result_a is True
+    assert result_b is True
+    # With the lock in place the two modal_request events must be emitted
+    # sequentially (one completes before the other starts), so exactly two
+    # distinct request IDs must have been emitted.
+    assert len(emitted_order) == 2
+    assert emitted_order[0] != emitted_order[1]