diff --git a/xrspatial/pathfinding.py b/xrspatial/pathfinding.py
index 76beb12e..9e836fdf 100644
--- a/xrspatial/pathfinding.py
+++ b/xrspatial/pathfinding.py
@@ -16,12 +16,18 @@
 
 from xrspatial.cost_distance import _heap_push, _heap_pop
 from xrspatial.utils import (
+    _validate_raster,
     get_dataarray_resolution, ngjit,
     has_cuda_and_cupy, is_cupy_array, is_dask_cupy, has_dask_array,
 )
 
 NONE = -1
 
+# Maximum waypoint count for multi_stop_search.  optimize_order builds an
+# N x N distance matrix and runs N(N-1)/2 A* calls (O(N^3) when stitched
+# with 2-opt), so unbounded N is a CPU DoS.
+_MAX_WAYPOINTS = 1000
+
 
 def _get_pixel_id(point, raster, xdim=None, ydim=None):
     # get location in `raster` pixel space for `point` in y-x coordinate space
@@ -894,8 +900,12 @@ def a_star_search(surface: xr.DataArray,
         >>> path_agg = a_star_search(agg, start, goal, barriers, 'lon', 'lat')
     """
 
-    if surface.ndim != 2:
-        raise ValueError("input `surface` must be 2D")
+    _validate_raster(surface, func_name='a_star_search',
+                     name='surface', ndim=2)
+
+    if friction is not None:
+        _validate_raster(friction, func_name='a_star_search',
+                         name='friction', ndim=2)
 
     if surface.dims != (y, x):
         raise ValueError("`surface.coords` should be named as coordinates:"
@@ -1370,12 +1380,23 @@ def multi_stop_search(surface: xr.DataArray,
         unreachable.
     """
     # --- Input validation ---
-    if surface.ndim != 2:
-        raise ValueError("input `surface` must be 2D")
+    _validate_raster(surface, func_name='multi_stop_search',
+                     name='surface', ndim=2)
+
+    if friction is not None:
+        _validate_raster(friction, func_name='multi_stop_search',
+                         name='friction', ndim=2)
 
     if len(waypoints) < 2:
         raise ValueError("at least 2 waypoints are required")
 
+    if len(waypoints) > _MAX_WAYPOINTS:
+        raise ValueError(
+            f"multi_stop_search() supports at most {_MAX_WAYPOINTS} "
+            f"waypoints, got {len(waypoints)}.  optimize_order is "
+            f"O(N^3) so larger lists can hang the worker."
+        )
+
     for idx, wp in enumerate(waypoints):
         if len(wp) != 2:
             raise ValueError(
diff --git a/xrspatial/tests/test_pathfinding.py b/xrspatial/tests/test_pathfinding.py
index 91eab85e..4fccd29f 100644
--- a/xrspatial/tests/test_pathfinding.py
+++ b/xrspatial/tests/test_pathfinding.py
@@ -1004,3 +1004,55 @@ def test_multi_stop_cupy_matches_numpy():
         path_np.values,
         equal_nan=True, atol=1e-10,
     )
+
+
+# =====================================================================
+# Issue #1439: input validation
+# =====================================================================
+
+import xarray as _xr_for_validation
+
+
+class TestPathfindingInputValidation:
+    """a_star_search / multi_stop_search reject bad surface and waypoint cap (#1439)."""
+
+    @staticmethod
+    def _good_surface():
+        return _xr_for_validation.DataArray(
+            np.zeros((10, 10), dtype=np.float64),
+            dims=('y', 'x'),
+            coords={'y': np.arange(10), 'x': np.arange(10)},
+        )
+
+    def test_a_star_rejects_non_dataarray_surface(self):
+        from xrspatial.pathfinding import a_star_search
+        with pytest.raises(TypeError, match="xarray.DataArray"):
+            a_star_search(np.zeros((10, 10)), (0, 0), (5, 5))
+
+    def test_a_star_rejects_complex_dtype_surface(self):
+        from xrspatial.pathfinding import a_star_search
+        bad = _xr_for_validation.DataArray(
+            np.zeros((10, 10), dtype=np.complex128),
+            dims=('y', 'x'),
+            coords={'y': np.arange(10), 'x': np.arange(10)},
+        )
+        with pytest.raises(ValueError, match="real numeric"):
+            a_star_search(bad, (0, 0), (5, 5))
+
+    def test_a_star_rejects_non_dataarray_friction(self):
+        from xrspatial.pathfinding import a_star_search
+        s = self._good_surface()
+        with pytest.raises(TypeError, match="xarray.DataArray"):
+            a_star_search(s, (0, 0), (5, 5), friction=np.ones((10, 10)))
+
+    def test_multi_stop_rejects_non_dataarray_surface(self):
+        from xrspatial.pathfinding import multi_stop_search
+        with pytest.raises(TypeError, match="xarray.DataArray"):
+            multi_stop_search(np.zeros((10, 10)), [(0, 0), (5, 5)])
+
+    def test_multi_stop_caps_waypoints(self):
+        from xrspatial.pathfinding import multi_stop_search, _MAX_WAYPOINTS
+        s = self._good_surface()
+        too_many = [(i % 10, (i * 7) % 10) for i in range(_MAX_WAYPOINTS + 1)]
+        with pytest.raises(ValueError, match=f"at most {_MAX_WAYPOINTS}"):
+            multi_stop_search(s, too_many)