diff --git a/src/openflexure_microscope_server/things/autofocus.py b/src/openflexure_microscope_server/things/autofocus.py
index 23c5560f..92eabd41 100644
--- a/src/openflexure_microscope_server/things/autofocus.py
+++ b/src/openflexure_microscope_server/things/autofocus.py
@@ -134,7 +134,7 @@ class SharpnessDataArrays(BaseModel):
     jpeg_times: NDArray
     jpeg_sizes: NDArray
     stage_times: NDArray
-    stage_positions: NDArray
+    stage_positions: list[dict[str, int]]
 
 
 class AutofocusThing(Thing):