diff --git a/ironic_python_agent/encoding.py b/ironic_python_agent/encoding.py
index 715d13411..b1b44cd19 100644
--- a/ironic_python_agent/encoding.py
+++ b/ironic_python_agent/encoding.py
@@ -15,6 +15,8 @@
 import json
 import uuid
 
+from ironic_lib import exception as lib_exc
+
 
 class Serializable(object):
     """Base class for things that can be serialized."""
@@ -43,6 +45,14 @@ class SerializableComparable(Serializable):
         return self.serialize() != other.serialize()
 
 
+def serialize_lib_exc(exc):
+    """Serialize an ironic-lib exception."""
+    return {'type': exc.__class__.__name__,
+            'code': exc.code,
+            'message': str(exc),
+            'details': ''}
+
+
 class RESTJSONEncoder(json.JSONEncoder):
     """A slightly customized JSON encoder."""
     def encode(self, o):
@@ -68,5 +78,7 @@ class RESTJSONEncoder(json.JSONEncoder):
             return o.serialize()
         elif isinstance(o, uuid.UUID):
             return str(o)
+        elif isinstance(o, lib_exc.IronicException):
+            return serialize_lib_exc(o)
         else:
             return json.JSONEncoder.default(self, o)
diff --git a/ironic_python_agent/tests/unit/test_encoding.py b/ironic_python_agent/tests/unit/test_encoding.py
index 64cd9b636..862cd9e82 100644
--- a/ironic_python_agent/tests/unit/test_encoding.py
+++ b/ironic_python_agent/tests/unit/test_encoding.py
@@ -12,6 +12,10 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import json
+
+from ironic_lib import exception as lib_exc
+
 from ironic_python_agent import encoding
 from ironic_python_agent.tests.unit import base
 
@@ -59,3 +63,20 @@ class TestSerializableComparable(base.IronicAgentTest):
         # Ensure __hash__ is None
         obj = SerializableComparableTesting('hello', 'world')
         self.assertIsNone(obj.__hash__)
+
+
+class TestEncoder(base.IronicAgentTest):
+
+    encoder = encoding.RESTJSONEncoder()
+
+    def test_encoder(self):
+        expected = {'jack': 'hello', 'jill': 'world'}
+        obj = SerializableTesting('hello', 'world')
+        self.assertEqual(expected, json.loads(self.encoder.encode(obj)))
+
+    def test_ironic_lib(self):
+        obj = lib_exc.InstanceDeployFailure(reason='boom')
+        encoded = json.loads(self.encoder.encode(obj))
+        self.assertEqual(500, encoded['code'])
+        self.assertEqual('InstanceDeployFailure', encoded['type'])
+        self.assertIn('boom', encoded['message'])
diff --git a/releasenotes/notes/lib-exc-41ee122eb4a04bc4.yaml b/releasenotes/notes/lib-exc-41ee122eb4a04bc4.yaml
new file mode 100644
index 000000000..cb3e8c2f7
--- /dev/null
+++ b/releasenotes/notes/lib-exc-41ee122eb4a04bc4.yaml
@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    Fixes serializing exceptions originating from ironic-lib. Previously an
+    attempt to do so would result in a ``TypeError``, for example:
+    `Object of type 'InstanceDeployFailure' is not JSON serializable`.