diff --git a/heat/bmi_heat.py b/heat/bmi_heat.py
index c554b76..027fed3 100644
--- a/heat/bmi_heat.py
+++ b/heat/bmi_heat.py
@@ -300,15 +300,15 @@ def get_grid_shape(self, grid_id: int, shape: NDArray[np.int_]) -> NDArray[np.in
         return shape
 
     def get_grid_spacing(
-        self, grid_id: int, spacing: NDArray[np.float_]
-    ) -> NDArray[np.float_]:
+        self, grid_id: int, spacing: NDArray[np.float64]
+    ) -> NDArray[np.float64]:
         """Spacing of rows and columns of uniform rectilinear grid."""
         spacing[:] = self._model.spacing
         return spacing
 
     def get_grid_origin(
-        self, grid_id: int, origin: NDArray[np.float_]
-    ) -> NDArray[np.float_]:
+        self, grid_id: int, origin: NDArray[np.float64]
+    ) -> NDArray[np.float64]:
         """Origin of uniform rectilinear grid."""
         origin[:] = self._model.origin
         return origin
@@ -369,11 +369,11 @@ def get_grid_nodes_per_face(
     def get_grid_face_edges(self, grid: int, face_edges: NDArray[np.int_]) -> None:
         raise NotImplementedError("get_grid_face_edges")
 
-    def get_grid_x(self, grid: int, x: NDArray[np.float_]) -> None:
+    def get_grid_x(self, grid: int, x: NDArray[np.float64]) -> None:
         raise NotImplementedError("get_grid_x")
 
-    def get_grid_y(self, grid: int, y: NDArray[np.float_]) -> None:
+    def get_grid_y(self, grid: int, y: NDArray[np.float64]) -> None:
         raise NotImplementedError("get_grid_y")
 
-    def get_grid_z(self, grid: int, z: NDArray[np.float_]) -> None:
+    def get_grid_z(self, grid: int, z: NDArray[np.float64]) -> None:
         raise NotImplementedError("get_grid_z")
diff --git a/heat/heat.py b/heat/heat.py
index fa31bc1..3d4496d 100644
--- a/heat/heat.py
+++ b/heat/heat.py
@@ -10,12 +10,12 @@
 
 
 def solve_2d(
-    temp: NDArray[np.float_],
+    temp: NDArray[np.float64],
     spacing: tuple[float, ...],
-    out: NDArray[np.float_] | None = None,
+    out: NDArray[np.float64] | None = None,
     alpha: float = 1.0,
     time_step: float = 1.0,
-) -> NDArray[np.float_]:
+) -> NDArray[np.float64]:
     """Solve the 2D Heat Equation on a uniform mesh.
 
     Parameters
@@ -127,7 +127,7 @@ def time(self) -> float:
         return self._time
 
     @property
-    def temperature(self) -> NDArray[np.float_]:
+    def temperature(self) -> NDArray[np.float64]:
         """Temperature of the plate."""
         return self._temperature