diff --git a/stix2/test/v20/test_properties.py b/stix2/test/v20/test_properties.py
index 3ff207a..9e4b6e1 100644
--- a/stix2/test/v20/test_properties.py
+++ b/stix2/test/v20/test_properties.py
@@ -138,6 +138,11 @@ def test_reference_property_blacklist_type():
             "identity--8a8e8758-f92c-4058-ba38-f061cd42a0cf", True,
         )
 
+    with pytest.raises(CustomContentError):
+        ref_prop.clean(
+            "some-type--8a8e8758-f92c-4058-ba38-f061cd42a0cf", False,
+        )
+
 
 @pytest.mark.parametrize(
     "d", [
diff --git a/stix2/test/v20/test_report.py b/stix2/test/v20/test_report.py
index 53707ce..2de9363 100644
--- a/stix2/test/v20/test_report.py
+++ b/stix2/test/v20/test_report.py
@@ -4,6 +4,7 @@ import pytest
 import pytz
 
 import stix2
+from stix2.exceptions import InvalidValueError
 
 from .constants import (
     CAMPAIGN_ID, IDENTITY_ID, INDICATOR_ID, INDICATOR_KWARGS, RELATIONSHIP_ID,
@@ -133,3 +134,30 @@ def test_parse_report(data):
     assert rept.name == "The Black Vine Cyberespionage Group"
 
 # TODO: Add other examples
+
+
+def test_report_on_custom():
+    with pytest.raises(InvalidValueError):
+        stix2.v20.Report(
+            name="my report",
+            labels=["a label"],
+            published="2016-01-20T17:00:00Z",
+            object_refs=[
+                "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7",
+                "some-type--2672975a-ce1e-4473-a1c6-0d79868930c7"
+            ]
+        )
+
+    report = stix2.v20.Report(
+        name="my report",
+        labels=["a label"],
+        published="2016-01-20T17:00:00Z",
+        object_refs=[
+            "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7",
+            "some-type--2672975a-ce1e-4473-a1c6-0d79868930c7"
+        ],
+        allow_custom=True,
+    )
+
+    assert "some-type--2672975a-ce1e-4473-a1c6-0d79868930c7" \
+       in report.object_refs
diff --git a/stix2/test/v21/test_properties.py b/stix2/test/v21/test_properties.py
index 9914bd1..d2e2694 100644
--- a/stix2/test/v21/test_properties.py
+++ b/stix2/test/v21/test_properties.py
@@ -159,6 +159,11 @@ def test_reference_property_blacklist_type():
             "identity--8a8e8758-f92c-4058-ba38-f061cd42a0cf", True,
         )
 
+    with pytest.raises(CustomContentError):
+        ref_prop.clean(
+            "some-type--8a8e8758-f92c-4058-ba38-f061cd42a0cf", False,
+        )
+
 
 @pytest.mark.parametrize(
     "d", [
diff --git a/stix2/test/v21/test_report.py b/stix2/test/v21/test_report.py
index e54e11d..69af096 100644
--- a/stix2/test/v21/test_report.py
+++ b/stix2/test/v21/test_report.py
@@ -9,6 +9,7 @@ from .constants import (
     CAMPAIGN_ID, IDENTITY_ID, INDICATOR_ID, INDICATOR_KWARGS, RELATIONSHIP_ID,
     REPORT_ID,
 )
+from stix2.exceptions import InvalidValueError
 
 EXPECTED = """{
     "type": "report",
@@ -135,4 +136,27 @@ def test_parse_report(data):
     assert rept.report_types == ["campaign"]
     assert rept.name == "The Black Vine Cyberespionage Group"
 
-# TODO: Add other examples
+
+def test_report_on_custom():
+    with pytest.raises(InvalidValueError):
+        stix2.v21.Report(
+            name="my report",
+            published="2016-01-20T17:00:00Z",
+            object_refs=[
+                "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7",
+                "some-type--2672975a-ce1e-4473-a1c6-0d79868930c7"
+            ]
+        )
+
+    report = stix2.v21.Report(
+        name="my report",
+        published="2016-01-20T17:00:00Z",
+        object_refs=[
+            "indicator--a740531e-63ff-4e49-a9e1-a0a3eed0e3e7",
+            "some-type--2672975a-ce1e-4473-a1c6-0d79868930c7"
+        ],
+        allow_custom=True,
+    )
+
+    assert "some-type--2672975a-ce1e-4473-a1c6-0d79868930c7" \
+       in report.object_refs
diff --git a/stix2/v20/sdo.py b/stix2/v20/sdo.py
index 538558a..3c854e0 100644
--- a/stix2/v20/sdo.py
+++ b/stix2/v20/sdo.py
@@ -235,7 +235,7 @@ class Report(_DomainObject):
         ('name', StringProperty(required=True)),
         ('description', StringProperty()),
         ('published', TimestampProperty(required=True)),
-        ('object_refs', ListProperty(ReferenceProperty(valid_types=["SCO", "SDO", "SRO"], spec_version='2.0'), required=True)),
+        ('object_refs', ListProperty(ReferenceProperty(invalid_types=[], spec_version='2.0'), required=True)),
         ('revoked', BooleanProperty(default=lambda: False)),
         ('labels', ListProperty(StringProperty, required=True)),
         ('external_references', ListProperty(ExternalReference)),
diff --git a/stix2/v21/sdo.py b/stix2/v21/sdo.py
index d0b6077..3b81e43 100644
--- a/stix2/v21/sdo.py
+++ b/stix2/v21/sdo.py
@@ -646,7 +646,7 @@ class Report(_DomainObject):
         ('description', StringProperty()),
         ('report_types', ListProperty(StringProperty)),
         ('published', TimestampProperty(required=True)),
-        ('object_refs', ListProperty(ReferenceProperty(valid_types=["SCO", "SDO", "SRO"], spec_version='2.1'), required=True)),
+        ('object_refs', ListProperty(ReferenceProperty(invalid_types=[], spec_version='2.1'), required=True)),
         ('revoked', BooleanProperty(default=lambda: False)),
         ('labels', ListProperty(StringProperty)),
         ('confidence', IntegerProperty()),