diff --git a/python/ray/tune/trial_runner.py b/python/ray/tune/trial_runner.py
index 7382065ab..9ecfcb540 100644
--- a/python/ray/tune/trial_runner.py
+++ b/python/ray/tune/trial_runner.py
@@ -45,11 +45,18 @@ def _find_newest_ckpt(ckpt_dir):
 class _TuneFunctionEncoder(json.JSONEncoder):
     def default(self, obj):
         if isinstance(obj, function):
-            return {
-                "_type": "function",
-                "value": binary_to_hex(cloudpickle.dumps(obj))
-            }
-        return super(_TuneFunctionEncoder, self).default(obj)
+            return self._to_cloudpickle(obj)
+        try:
+            return super(_TuneFunctionEncoder, self).default(obj)
+        except Exception:
+            logger.debug("Unable to encode. Falling back to cloudpickle.")
+            return self._to_cloudpickle(obj)
+
+    def _to_cloudpickle(self, obj):
+        return {
+            "_type": "CLOUDPICKLE_FALLBACK",
+            "value": binary_to_hex(cloudpickle.dumps(obj))
+        }
 
 
 class _TuneFunctionDecoder(json.JSONDecoder):
@@ -58,10 +65,13 @@ class _TuneFunctionDecoder(json.JSONDecoder):
             self, object_hook=self.object_hook, *args, **kwargs)
 
     def object_hook(self, obj):
-        if obj.get("_type") == "function":
-            return cloudpickle.loads(hex_to_binary(obj["value"]))
+        if obj.get("_type") == "CLOUDPICKLE_FALLBACK":
+            return self._from_cloudpickle(obj)
         return obj
 
+    def _from_cloudpickle(self, obj):
+        return cloudpickle.loads(hex_to_binary(obj["value"]))
+
 
 class TrialRunner(object):
     """A TrialRunner implements the event loop for scheduling trials on Ray.