diff --git a/viser/_gui_api.py b/viser/_gui_api.py
index 768b1ae3d..5182a36d4 100644
--- a/viser/_gui_api.py
+++ b/viser/_gui_api.py
@@ -339,7 +339,7 @@ def add_gui_vector2(
         id = _make_unique_id()
 
         if step is None:
-            possible_steps = []
+            possible_steps: List[float] = []
             possible_steps.extend([_compute_step(x) for x in initial_value])
             if min is not None:
                 possible_steps.extend([_compute_step(x) for x in min])
@@ -384,7 +384,7 @@ def add_gui_vector3(
         id = _make_unique_id()
 
         if step is None:
-            possible_steps = []
+            possible_steps: List[float] = []
             possible_steps.extend([_compute_step(x) for x in initial_value])
             if min is not None:
                 possible_steps.extend([_compute_step(x) for x in min])