diff --git a/tests/conftest.py b/tests/conftest.py
index fbdb723..c265f6a 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -18,6 +18,7 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 
+import numpy as np
 import os
 from prpy.ffmpeg.probe import probe_video
 from prpy.ffmpeg.readwrite import read_video_from_path
@@ -52,7 +53,7 @@ def test_video_faces(request):
   test_video_fps = request.getfixturevalue('test_video_fps')
   boxes, _ = det(test_video_ndarray, fps=test_video_fps)
   boxes = (boxes * [test_video_ndarray.shape[2], test_video_ndarray.shape[1], test_video_ndarray.shape[2], test_video_ndarray.shape[1]]).astype(int)
-  return boxes[:,0]
+  return boxes[:,0].astype(np.int64)
 
 @pytest.fixture(scope='session')
 def test_dev_api_key():
diff --git a/vitallens/client.py b/vitallens/client.py
index c3d8ec1..2fc151c 100644
--- a/vitallens/client.py
+++ b/vitallens/client.py
@@ -160,7 +160,7 @@ def __call__(
         logging.warn("No faces to analyze")
         return []
       # Convert to absolute units
-      faces = (faces_rel * [width, height, width, height]).astype(int)
+      faces = (faces_rel * [width, height, width, height]).astype(np.int64)
       # Face axis first
       faces = np.transpose(faces, (1, 0, 2))
     # Check if the faces are valid
diff --git a/vitallens/methods/simple_rppg_method.py b/vitallens/methods/simple_rppg_method.py
index 0d24305..43e2fea 100644
--- a/vitallens/methods/simple_rppg_method.py
+++ b/vitallens/methods/simple_rppg_method.py
@@ -62,7 +62,7 @@ def __call__(
 
     Args:
       frames: The video frames. Shape (n_frames, h, w, c)
-      faces: The face detection boxes. Shape (n_frames, 4) in form (x0, y0, x1, y1)
+      faces: The face detection boxes as np.int64. Shape (n_frames, 4) in form (x0, y0, x1, y1)
       fps: The rate at which video was sampled.
       override_fps_target: Override the method's default inference fps (optional).
     Returns:
diff --git a/vitallens/methods/vitallens.py b/vitallens/methods/vitallens.py
index a8ca58b..d60ea1d 100644
--- a/vitallens/methods/vitallens.py
+++ b/vitallens/methods/vitallens.py
@@ -61,7 +61,7 @@ def __call__(
     Args:
       frames: The video to analyze. Either a np.ndarray of shape (n_frames, h, w, 3)
         in unscaled uint8 RGB format, or a path to a video file.
-      faces: The face detection boxes. Shape (n_frames, 4) in form (x0, y0, x1, y1)
+      faces: The face detection boxes as np.int64. Shape (n_frames, 4) in form (x0, y0, x1, y1)
       fps: The rate at which video was sampled.
       override_fps_target: Override the method's default inference fps (optional).
     Returns:
diff --git a/vitallens/utils.py b/vitallens/utils.py
index 412eae9..1b7e414 100644
--- a/vitallens/utils.py
+++ b/vitallens/utils.py
@@ -182,9 +182,9 @@ def check_faces(
   if faces is None:
     # Assume that each entire frame is a single face
     logging.info("No faces given - assuming that frames have been cropped to a single face")
-    faces = np.tile(np.asarray([0, 0, w, h]), (n_frames, 1))[np.newaxis] # (1, n_frames, 4)
+    faces = np.tile(np.asarray([0, 0, w, h], dtype=np.int64), (n_frames, 1))[np.newaxis] # (1, n_frames, 4)
   else:
-    faces = np.asarray(faces)
+    faces = np.asarray(faces, dtype=np.int64)
     if faces.shape[-1] != 4: raise ValueError("Face detections must be in flat point form")
     if len(faces.shape) == 1:
       # Single face detection given - repeat for n_frames