diff --git a/src/dodal/parameters/experiment_parameter_base.py b/src/dodal/parameters/experiment_parameter_base.py
index 30da3ac264..ccfd758e4a 100644
--- a/src/dodal/parameters/experiment_parameter_base.py
+++ b/src/dodal/parameters/experiment_parameter_base.py
@@ -3,5 +3,5 @@
 
 class AbstractExperimentParameterBase(ABC):
     @abstractmethod
-    def get_num_images(self):
+    def get_num_images(self) -> int:
         pass