diff --git a/src/ophyd_async/fastcs/eiger/_eiger_io.py b/src/ophyd_async/fastcs/eiger/_eiger_io.py
index e9c2fb677a..35ad7b83f2 100644
--- a/src/ophyd_async/fastcs/eiger/_eiger_io.py
+++ b/src/ophyd_async/fastcs/eiger/_eiger_io.py
@@ -29,7 +29,7 @@ class EigerDetectorIO(Device):
     frame_time: SignalRW[float]
     nimages: SignalRW[int]
     ntrigger: SignalRW[int]
-    nexpi: SignalRW[int]
+    nexpi: SignalRW[int] | None
     trigger_mode: SignalRW[str]
     roi_mode: SignalRW[str]
     photon_energy: SignalRW[float]