diff --git a/world.py b/world.py
index eee7ef3..e172bf4 100644
--- a/world.py
+++ b/world.py
@@ -278,7 +278,7 @@ def check_valid_step(self, start_pos, end_pos, barrier_dir):
 
         Parameters
         ----------
-        start_pos : tuple
+        start_pos : np.ndarray
             The start position of the agent.
         end_pos : np.ndarray
             The end position of the agent.