diff --git a/svc/src/hudctrl/api.py b/svc/src/hudctrl/api.py
index 82d0478..c41f986 100644
--- a/svc/src/hudctrl/api.py
+++ b/svc/src/hudctrl/api.py
@@ -75,12 +75,18 @@ async def list_screens():
 
 
 @app.post(
-    '/screen/{number}/refresh',
+    '/screen/{name}/refresh',
     response_class=fastapi.Response,
     status_code=fastapi.status.HTTP_204_NO_CONTENT,
 )
-async def refresh_screen(number: int):
-    await svc.refresh_screen(number)
+async def refresh_screen(name: str):
+    try:
+        await svc.refresh_screen(name)
+    except KeyError:
+        raise fastapi.HTTPException(
+            fastapi.status.HTTP_404_NOT_FOUND,
+            detail=f'No such screen: {name}',
+        ) from None
 
 
 @app.on_event('shutdown')
diff --git a/svc/src/hudctrl/hud.py b/svc/src/hudctrl/hud.py
index ee85686..85e21c7 100644
--- a/svc/src/hudctrl/hud.py
+++ b/svc/src/hudctrl/hud.py
@@ -31,6 +31,7 @@ class HUDService:
         self.monitor_config: Optional[MonitorConfig] = None
         self.marionette: Optional[Marionette] = None
         self.urls: Dict[str, str] = {}
+        self.windows: Dict[str, str] = {}
 
         self.urls_file = Path('urls.json')
 
@@ -49,6 +50,7 @@ class HUDService:
 
     async def initialize(self) -> None:
         assert self.marionette
+        self.windows.clear()
         if not self.monitor_config:
             raise NoMonitorConfig(
                 'Cannot initialize display: No monitor config supplied'
@@ -71,6 +73,7 @@ class HUDService:
                 continue
             if window is None:
                 window = await self.marionette.new_window('window')
+            self.windows[monitor.name] = window
             await self.marionette.switch_to_window(window)
             await self.marionette.set_window_rect(
                 x=monitor.pos_x,
@@ -107,10 +110,9 @@ class HUDService:
                     dict,
                 )
 
-    async def refresh_screen(self, number: int) -> None:
+    async def refresh_screen(self, name: str) -> None:
         assert self.marionette
-        windows = await self.marionette.get_window_handles()
-        await self.marionette.switch_to_window(windows[number])
+        await self.marionette.switch_to_window(self.windows[name])
         await self.marionette.refresh()
 
     async def set_display(self, host: str, port: int) -> None: