diff --git a/clients/python/sliderule/session.py b/clients/python/sliderule/session.py
index 18f7fbc5f..0819eb148 100644
--- a/clients/python/sliderule/session.py
+++ b/clients/python/sliderule/session.py
@@ -105,6 +105,21 @@
     12: "STRING"
 }
 
+def _json_encoder(obj):
+    if isinstance(obj, (bytes, bytearray)):
+        return obj.decode('utf-8')
+    if isinstance(obj, numpy.integer):
+        return int(obj)
+    if isinstance(obj, numpy.floating):
+        return float(obj)
+    if isinstance(obj, numpy.ndarray):
+        return obj.tolist()
+    if isinstance(obj, numpy.bool_):
+        return bool(obj)
+    if isinstance(obj, numpy.void):
+        return None
+    return obj
+
 ###############################################################################
 # CLASSES
 ###############################################################################
@@ -211,7 +226,7 @@ def source (self, api, parm=None, stream=False, callbacks=None, path="/source",
 
         # Construct Payload
         if isinstance(parm, dict):
-            payload = json.dumps(parm)
+            payload = json.dumps(parm, default=_json_encoder)
         else:
             payload = parm
 
diff --git a/clients/python/tests/test_apis.py b/clients/python/tests/test_apis.py
index 9d772b076..8f5e55c27 100644
--- a/clients/python/tests/test_apis.py
+++ b/clients/python/tests/test_apis.py
@@ -1,8 +1,12 @@
 """Tests for sliderule APIs."""
 
+import json
+import numpy as np
 import pytest
+import requests
 import sliderule
 from sliderule import icesat2
+from sliderule.session import Session
 from pathlib import Path
 import os
 
@@ -129,3 +133,31 @@ def test_toregion(self):
         region = sliderule.toregion(os.path.join(TESTDIR, 'data/polygon.geojson'))
         assert len(region["poly"]) == 5 # 5 coordinate pairs
         assert {'lon', 'lat'} <= region["poly"][0].keys()
+
+    def test_toregion_int_coords_json_serializable(self):
+        region = sliderule.toregion([
+            {"lon": -120, "lat": -25},
+            {"lon": -95, "lat": -25},
+            {"lon": -95, "lat": 0},
+            {"lon": -120, "lat": 0},
+            {"lon": -120, "lat": -25},
+        ])
+        json.dumps(region["poly"])
+
+    def test_toregion_numpy_int_coords_request_serializable(self, monkeypatch):
+        session = Session()
+
+        def fake_get(*args, **kwargs):
+            raise requests.ConnectionError("blocked")
+
+        monkeypatch.setattr(session.session, "get", fake_get)
+
+        poly = [
+            {"lon": np.int64(-120), "lat": np.int64(-25)},
+            {"lon": np.int64(-95), "lat": np.int64(-25)},
+            {"lon": np.int64(-95), "lat": np.int64(0)},
+            {"lon": np.int64(-120), "lat": np.int64(0)},
+            {"lon": np.int64(-120), "lat": np.int64(-25)},
+        ]
+        rsps = session.source("version", {"poly": poly}, stream=False)
+        assert rsps == "Connection error"