diff --git a/stix2/test/test_custom.py b/stix2/test/test_custom.py
index a14503f..b45670f 100644
--- a/stix2/test/test_custom.py
+++ b/stix2/test/test_custom.py
@@ -479,6 +479,27 @@ def test_custom_extension_wrong_observable_type():
     assert 'Cannot determine extension type' in excinfo.value.reason
 
 
+@pytest.mark.parametrize("data", [
+    """{
+    "keys": [
+        {
+            "test123": 123,
+            "test345": "aaaa"
+        }
+    ]
+}""",
+])
+def test_custom_extension_with_list_and_dict_properties_observable_type(data):
+    @stix2.observables.CustomExtension(stix2.UserAccount, 'some-extension', [
+        ('keys', stix2.properties.ListProperty(stix2.properties.DictionaryProperty, required=True))
+    ])
+    class SomeCustomExtension:
+        pass
+
+    example = SomeCustomExtension(keys=[{'test123': 123, 'test345': 'aaaa'}])
+    assert data == str(example)
+
+
 def test_custom_extension_invalid_observable():
     # These extensions are being applied to improperly-created Observables.
     # The Observable classes should have been created with the CustomObservable decorator.
diff --git a/stix2/utils.py b/stix2/utils.py
index 9febd78..4ef3d23 100644
--- a/stix2/utils.py
+++ b/stix2/utils.py
@@ -166,7 +166,7 @@ def get_dict(data):
 def find_property_index(obj, properties, tuple_to_find):
     """Recursively find the property in the object model, return the index
     according to the _properties OrderedDict. If it's a list look for
-    individual objects.
+    individual objects. Returns and integer indicating its location
     """
     from .base import _STIXBase
     try:
@@ -183,6 +183,11 @@ def find_property_index(obj, properties, tuple_to_find):
                                                   tuple_to_find)
                         if val is not None:
                             return val
+                    elif isinstance(item, dict):
+                        for idx, val in enumerate(sorted(item)):
+                            if (tuple_to_find[0] == val and
+                                    item.get(val) == tuple_to_find[1]):
+                                return idx
             elif isinstance(pv, dict):
                 if pv.get(tuple_to_find[0]) is not None:
                     try: