diff --git a/cadence/_internal/activity/_activity_executor.py b/cadence/_internal/activity/_activity_executor.py
index e37e736..56f717d 100644
--- a/cadence/_internal/activity/_activity_executor.py
+++ b/cadence/_internal/activity/_activity_executor.py
@@ -57,7 +57,7 @@ async def _report_failure(self, task: PollForActivityTaskResponse, error: Except
             _logger.exception('Exception reporting activity failure')
 
     async def _report_success(self, task: PollForActivityTaskResponse, result: Any):
-        as_payload = await self._data_converter.to_data(result)
+        as_payload = await self._data_converter.to_data([result])
 
         try:
             await self._client.worker_stub.RespondActivityTaskCompleted(RespondActivityTaskCompletedRequest(
diff --git a/cadence/data_converter.py b/cadence/data_converter.py
index e88680f..350848e 100644
--- a/cadence/data_converter.py
+++ b/cadence/data_converter.py
@@ -5,6 +5,7 @@
 from json import JSONDecoder
 from msgspec import json, convert
 
+_SPACE = ' '.encode()
 
 class DataConverter(Protocol):
 
@@ -19,33 +20,24 @@ async def to_data(self, values: List[Any]) -> Payload:
 class DefaultDataConverter(DataConverter):
     def __init__(self) -> None:
         self._encoder = json.Encoder()
-        self._decoder = json.Decoder()
-        self._fallback_decoder = JSONDecoder(strict=False)
+        # Need to use std lib decoder in order to decode the custom whitespace delimited data format
+        self._decoder = JSONDecoder(strict=False)
 
 
     async def from_data(self, payload: Payload, type_hints: List[Type | None]) -> List[Any]:
         if not payload.data:
             return DefaultDataConverter._convert_into([], type_hints)
 
-        if len(type_hints) > 1:
-            payload_str = payload.data.decode()
-            # Handle payloads from the Go client, which are a series of json objects rather than a json array
-            if not payload_str.startswith("["):
-                return self._decode_whitespace_delimited(payload_str, type_hints)
-            else:
-                as_list = self._decoder.decode(payload_str)
-                return DefaultDataConverter._convert_into(as_list, type_hints)
-
-        as_value = self._decoder.decode(payload.data)
-        return DefaultDataConverter._convert_into([as_value], type_hints)
+        payload_str = payload.data.decode()
 
+        return self._decode_whitespace_delimited(payload_str, type_hints)
 
     def _decode_whitespace_delimited(self, payload: str, type_hints: List[Type | None]) -> List[Any]:
         results: List[Any] = []
         start, end = 0, len(payload)
         while start < end and len(results) < len(type_hints):
             remaining = payload[start:end]
-            (value, value_end) = self._fallback_decoder.raw_decode(remaining)
+            (value, value_end) = self._decoder.raw_decode(remaining)
             start += value_end + 1
             results.append(value)
 
@@ -76,10 +68,11 @@ def _get_default(type_hint: Type) -> Any:
 
 
     async def to_data(self, values: List[Any]) -> Payload:
-        data_value = values
-        # Don't wrap single values in a json array
-        if len(values) == 1:
-            data_value = values[0]
+        result = bytearray()
+        for index, value in enumerate(values):
+            self._encoder.encode_into(value, result, -1)
+            if index < len(values) - 1:
+                result += _SPACE
 
-        return Payload(data=self._encoder.encode(data_value))
+        return Payload(data=bytes(result))
 
diff --git a/tests/cadence/_internal/activity/test_activity_executor.py b/tests/cadence/_internal/activity/test_activity_executor.py
index d6aba4d..abc02cb 100644
--- a/tests/cadence/_internal/activity/test_activity_executor.py
+++ b/tests/cadence/_internal/activity/test_activity_executor.py
@@ -82,7 +82,7 @@ async def activity_fn(first: str, second: str):
 
     executor = ActivityExecutor(client, 'task_list', 'identity', 1, reg.get_activity)
 
-    await executor.execute(fake_task("activity_type", '["hello", "world"]'))
+    await executor.execute(fake_task("activity_type", '"hello" "world"'))
 
     worker_stub.RespondActivityTaskCompleted.assert_called_once_with(RespondActivityTaskCompletedRequest(
         task_token=b'task_token',
diff --git a/tests/cadence/data_converter_test.py b/tests/cadence/data_converter_test.py
index cbc7ba6..068f3a5 100644
--- a/tests/cadence/data_converter_test.py
+++ b/tests/cadence/data_converter_test.py
@@ -23,31 +23,28 @@ class _TestDataClass:
             '"Hello" "world"', [str, str], ["Hello", "world"], id="space delimited"
         ),
         pytest.param(
-            '["Hello", "world"]', [str, str], ["Hello", "world"], id="json array"
+            "1", [int, int], [1, 0], id="ints"
         ),
         pytest.param(
-            "[1]", [int, int], [1, 0], id="ints"
+            "1.5", [float, float], [1.5, 0.0], id="floats"
         ),
         pytest.param(
-            "[1.5]", [float, float], [1.5, 0.0], id="floats"
+            "true", [bool, bool], [True, False], id="bools"
         ),
         pytest.param(
-            "[true]", [bool, bool], [True, False], id="bools"
+            '{"foo": "hello world", "bar": 42, "baz": {"bar": 43}}', [_TestDataClass, _TestDataClass], [_TestDataClass("hello world", 42, _TestDataClass(bar=43)), None], id="data classes"
         ),
         pytest.param(
-            '[{"foo": "hello world", "bar": 42, "baz": {"bar": 43}}]', [_TestDataClass, _TestDataClass], [_TestDataClass("hello world", 42, _TestDataClass(bar=43)), None], id="data classes"
+            '{"foo": "hello world"}', [dict, dict], [{"foo": "hello world"}, None], id="dicts"
         ),
         pytest.param(
-            '[{"foo": "hello world"}]', [dict, dict], [{"foo": "hello world"}, None], id="dicts"
+            '{"foo": 52}', [dict[str, int], dict], [{"foo": 52}, None], id="generic dicts"
         ),
         pytest.param(
-            '[{"foo": 52}]', [dict[str, int], dict], [{"foo": 52}, None], id="generic dicts"
+            '["hello"]', [list[str], list[str]], [["hello"], None], id="lists"
         ),
         pytest.param(
-            '[["hello"]]', [list[str], list[str]], [["hello"], None], id="lists"
-        ),
-        pytest.param(
-            '[["hello"]]', [set[str], set[str]], [{"hello"}, None], id="sets"
+            '["hello"]', [set[str], set[str]], [{"hello"}, None], id="sets"
         ),
         pytest.param(
             '["hello", "world"]', [list[str]], [["hello", "world"]], id="list"
@@ -56,10 +53,6 @@ class _TestDataClass:
             '{"foo": "bar"} {"bar": 100} ["hello"] "world"', [_TestDataClass, _TestDataClass, list[str], str],
             [_TestDataClass(foo="bar"), _TestDataClass(bar=100), ["hello"], "world"], id="space delimited mix"
         ),
-        pytest.param(
-            '[{"foo": "bar"},{"bar": 100},["hello"],"world"]', [_TestDataClass, _TestDataClass, list[str], str],
-            [_TestDataClass(foo="bar"), _TestDataClass(bar=100), ["hello"], "world"], id="json array mix"
-        ),
         pytest.param(
             "", [], [], id="no input expected"
         ),
@@ -67,7 +60,7 @@ class _TestDataClass:
             "", [str], [None], id="no input unexpected"
         ),
         pytest.param(
-            '["hello world", {"foo":"bar"}, 7]', [None, None, None], ["hello world", {"foo":"bar"}, 7], id="no type hints"
+            '"hello world" {"foo":"bar"} 7', [None, None, None], ["hello world", {"foo":"bar"}, 7], id="no type hints"
         ),
         pytest.param(
             '"hello" "world" "goodbye"', [str, str], ["hello", "world"],
@@ -75,7 +68,6 @@ class _TestDataClass:
         ),
     ]
 )
-@pytest.mark.asyncio
 async def test_data_converter_from_data(json: str, types: list[Type], expected: list[Any]) -> None:
     converter = DefaultDataConverter()
     actual = await converter.from_data(Payload(data=json.encode()), types)
@@ -88,18 +80,30 @@ async def test_data_converter_from_data(json: str, types: list[Type], expected:
             ["hello world"], '"hello world"', id="happy path"
         ),
         pytest.param(
-            ["hello", "world"], '["hello", "world"]', id="multiple values"
+            ["hello", "world"], '"hello" "world"', id="multiple values"
+        ),
+        pytest.param(
+            [[["hello"]], ["world"]], '[["hello"]] ["world"]', id="lists"
+        ),
+        pytest.param(
+            [1, 2, 10], '1 2 10', id="numeric values"
+        ),
+        pytest.param(
+            [True, False], 'true false', id="bool values"
+        ),
+        pytest.param(
+            [{'foo': 'foo', 'bar': 20}], '{"bar":20,"foo":"foo"}', id="dict values"
+        ),
+        pytest.param(
+            [{'foo', 'bar'}], '["bar","foo"]', id="set values"
         ),
         pytest.param(
-            [_TestDataClass()], '{"foo": "foo", "bar": -1, "baz": null}', id="data classes"
+            [_TestDataClass()], '{"foo":"foo","bar":-1,"baz":null}', id="data classes"
         ),
     ]
 )
-@pytest.mark.asyncio
 async def test_data_converter_to_data(values: list[Any], expected: str) -> None:
     converter = DefaultDataConverter()
+    converter._encoder = json.Encoder(order='deterministic')
     actual = await converter.to_data(values)
-    # Parse both rather than trying to compare strings
-    actual_parsed = json.decode(actual.data)
-    expected_parsed = json.decode(expected)
-    assert expected_parsed == actual_parsed
\ No newline at end of file
+    assert actual.data.decode() == expected
\ No newline at end of file