diff --git a/nameko_tracer/formatters.py b/nameko_tracer/formatters.py
index a2fb1c8..86e4c47 100644
--- a/nameko_tracer/formatters.py
+++ b/nameko_tracer/formatters.py
@@ -28,12 +28,21 @@ class ElasticsearchDocumentFormatter(JSONFormatter):
 
     """
 
+    extra_serialise_keys = (
+        constants.CONTEXT_DATA_KEY,
+        constants.REQUEST_KEY,
+        constants.RESPONSE_KEY)
+
     def format(self, record):
+
         trace = getattr(record, constants.TRACE_KEY)
-        trace[constants.CONTEXT_DATA_KEY] = serialise(
-            trace[constants.CONTEXT_DATA_KEY])
-        trace[constants.REQUEST_KEY] = serialise(
-            trace[constants.REQUEST_KEY])
-        trace[constants.RESPONSE_KEY] = serialise(
-            trace[constants.RESPONSE_KEY])
+
+        for key in self.extra_serialise_keys:
+            if key in trace:
+                trace[key] = serialise(trace[key])
+
+        if constants.ERROR_KEY in trace:
+            trace[constants.ERROR_KEY]['exc_args'] = serialise(
+                trace[constants.ERROR_KEY]['exc_args'])
+
         return serialise(trace)
diff --git a/tests/test_formatters.py b/tests/test_formatters.py
index d33bcd9..b1f2f6f 100644
--- a/tests/test_formatters.py
+++ b/tests/test_formatters.py
@@ -26,14 +26,45 @@ def test_json_serialiser_will_deal_with_datetime(input_, expected_output):
         formatters.JSONFormatter().format(log_record) == expected_output)
 
 
-def test_elasticsearch_document_serialiser():
+@pytest.mark.parametrize(
+    ('key', 'value_in', 'expected_value_out'),
+    (
+        (
+            constants.CONTEXT_DATA_KEY,
+            {'should': ('be', 'serialised')},
+            '{"should": ["be", "serialised"]}',
+        ),
+        (
+            constants.REQUEST_KEY,
+            ('should', 'be', 'serialised'),
+            '["should", "be", "serialised"]',
+        ),
+        (
+            constants.RESPONSE_KEY,
+            {'should': ('be', 'serialised')},
+            '{"should": ["be", "serialised"]}',
+        ),
+        (
+            constants.ERROR_KEY,
+            {
+                'exc_args': {'should': ('be', 'serialised')},
+                'spam': {'should': ['NOT', 'be', 'serialised']},
+            },
+            {
+                'exc_args': '{"should": ["be", "serialised"]}',
+                'spam': {'should': ['NOT', 'be', 'serialised']},
+            }
+        ),
+        (
+            'some-other-key',
+            {'should': ['NOT', 'be', 'serialised']},
+            {'should': ['NOT', 'be', 'serialised']},
+        ),
+    )
+)
+def test_elasticsearch_document_serialiser(key, value_in, expected_value_out):
 
-    trace = {
-        constants.CONTEXT_DATA_KEY: {'should': ('be', 'serialised')},
-        constants.REQUEST_KEY: ('should', 'be', 'serialised'),
-        constants.RESPONSE_KEY: {'should': ('be', 'serialised')},
-        'some-other-key': {'should': ['NOT', 'be', 'serialised']},
-    }
+    trace = {key: value_in}
 
     log_record = Mock()
     setattr(log_record, constants.TRACE_KEY, trace)
@@ -42,15 +73,4 @@ def test_elasticsearch_document_serialiser():
 
     document = json.loads(document)
 
-    assert (
-        document[constants.CONTEXT_DATA_KEY] ==
-        '{"should": ["be", "serialised"]}')
-    assert (
-        document[constants.REQUEST_KEY] ==
-        '["should", "be", "serialised"]')
-    assert (
-        document[constants.RESPONSE_KEY] ==
-        '{"should": ["be", "serialised"]}')
-    assert (
-        document['some-other-key'] ==
-        {'should': ['NOT', 'be', 'serialised']})
+    assert document[key] == expected_value_out