diff --git a/PathPlanning/TimeBasedPathPlanning/GridWithDynamicObstacles.py b/PathPlanning/TimeBasedPathPlanning/GridWithDynamicObstacles.py
index ccc2989001..7a35207aeb 100644
--- a/PathPlanning/TimeBasedPathPlanning/GridWithDynamicObstacles.py
+++ b/PathPlanning/TimeBasedPathPlanning/GridWithDynamicObstacles.py
@@ -200,6 +200,10 @@ def valid_position(self, position: Position, t: int) -> bool:
         if not self.inside_grid_bounds(position):
             return False
 
+        # Times outside the simulation window are not valid
+        if t < 0 or t >= self.time_limit:
+            return False
+
         # Check if position is not occupied at time t
         return self.reservation_matrix[position.x, position.y, t] == 0
 
diff --git a/tests/test_space_time_astar.py b/tests/test_space_time_astar.py
index 1194c61d2e..8380b22e11 100644
--- a/tests/test_space_time_astar.py
+++ b/tests/test_space_time_astar.py
@@ -5,6 +5,7 @@
 )
 from PathPlanning.TimeBasedPathPlanning import SpaceTimeAStar as m
 import numpy as np
+import pytest
 import conftest
 
 
@@ -28,5 +29,21 @@ def test_1():
 
     assert path.expanded_node_count < 1000
 
+def test_no_path_within_time_limit():
+    # Goal is farther away than the time limit allows, so planning should
+    # fail cleanly instead of indexing past the reservation matrix
+    start = Position(1, 1)
+    goal = Position(9, 9)
+    grid = Grid(
+        np.array([11, 11]),
+        num_obstacles=0,
+        obstacle_avoid_points=[start, goal],
+        time_limit=5,
+    )
+
+    m.show_animation = False
+    with pytest.raises(Exception, match="No path found"):
+        m.SpaceTimeAStar.plan(grid, start, goal)
+
 if __name__ == "__main__":
     conftest.run_this_test(__file__)