diff --git a/sbws/util/state.py b/sbws/util/state.py
index 50e6a66ef43402e970822c6ebbc2de5649635b99..b6614a7082de6cf37bfc2b8529705dec58d50267 100644
--- a/sbws/util/state.py
+++ b/sbws/util/state.py
@@ -2,6 +2,8 @@ from sbws.util.filelock import FileLock
 import os
 import json
 
+from .json import CustomDecoder, CustomEncoder
+
 
 class State:
     """
@@ -48,12 +50,12 @@ class State:
             return {}
         with FileLock(self._fname):
             with open(self._fname, 'rt') as fd:
-                return json.load(fd)
+                return json.load(fd, cls=CustomDecoder)
 
     def _write(self):
         with FileLock(self._fname):
             with open(self._fname, 'wt') as fd:
-                return json.dump(self._state, fd, indent=4)
+                return json.dump(self._state, fd, indent=4, cls=CustomEncoder)
 
     def __len__(self):
         self._state = self._read()
diff --git a/tests/unit/util/test_state.py b/tests/unit/util/test_state.py
index a57768dc68d62c61916b0c9882194309c3a9b154..d08a4a960468217382c5d2e86ccb9d95d2aaf428 100644
--- a/tests/unit/util/test_state.py
+++ b/tests/unit/util/test_state.py
@@ -83,3 +83,11 @@ def test_two_instances(tmpdir):
     s1["x"] = "foo"
     s2["y"] = "bar"
     assert s2["x"] == "foo"
+
+
+def test_datetime_values(tmpdir):
+    import datetime
+    state = State(os.path.join(str(tmpdir), 'state.dat'))
+    now = datetime.datetime.utcnow().replace(microsecond=0)
+    state["datetimes"] = now
+    assert now == state["datetimes"]