diff --git a/src/aliby/tile/tiler.py b/src/aliby/tile/tiler.py
index 7bf99291c6a177d432d9199fcac9775a0b317a88..abfcb347f3a75474749d7d47dcb42e728ffe4f63 100644
--- a/src/aliby/tile/tiler.py
+++ b/src/aliby/tile/tiler.py
@@ -216,7 +216,7 @@ class Tiler(StepABC):
         image: da.core.Array,
         metadata: dict,
         parameters: TilerParameters,
-        trap_locs=None,
+        trap_locs: t.List[t.List[int]] = None,
     ):
         """
         Initialise Tiler
@@ -237,7 +237,7 @@ class Tiler(StepABC):
 
         self.ref_channel = self.get_channel_index(parameters.ref_channel)
 
-        self.trap_locs = trap_locs
+        self.trap_locs: t.List[t.List[int]] = trap_locs
         try:
             self.z_perchannel = {
                 ch: zsect
@@ -302,7 +302,7 @@ class Tiler(StepABC):
         cls,
         image,
         filepath: t.Union[str, PosixPath],
-        parameters: TilerParameters = None,
+        parameters: t.Optional[TilerParameters] = None,
     ):
         """
         Instantiate Tiler from hdf5 files
diff --git a/src/aliby/utils/vis_tools.py b/src/aliby/utils/vis_tools.py
index 7d688211cf5630a945ee2a2617f2a0cfcfd034bb..c6d4b7de7a483056741a150121f2cdfd59a02b30 100644
--- a/src/aliby/utils/vis_tools.py
+++ b/src/aliby/utils/vis_tools.py
@@ -108,7 +108,7 @@ def _dispatch_tile_reduction(how: t.Union[int, str, t.List[int]], axis=1):
         raise Exception(f"Invalid reduction {how}")
 
 
-def tile_like(arr1, arr2):
+def tile_like(arr1: np.ndarray, arr2: np.ndarray):
     """
     Tile the first two dimensions of arr1 (ND) to match arr2 (2D)
     """