diff --git a/stix2/test/v21/test_course_of_action.py b/stix2/test/v21/test_course_of_action.py
index ca8a303..5eea908 100644
--- a/stix2/test/v21/test_course_of_action.py
+++ b/stix2/test/v21/test_course_of_action.py
@@ -8,6 +8,7 @@ import stix2.utils
 
 COA_WITH_BIN_JSON = """{
     "type": "course-of-action",
+    "spec_version": "2.1",
     "id": "course-of-action--8e2e2d2b-17d4-4cbf-938f-98ee46b3cd3f",
     "created_by_ref": "identity--311b2d2d-f010-4473-83ec-1edf84858f4c",
     "created": "2016-04-06T20:03:48.000Z",
@@ -19,6 +20,7 @@ COA_WITH_BIN_JSON = """{
 
 COA_WITH_REF_JSON = """{
     "type": "course-of-action",
+    "spec_version": "2.1",
     "id": "course-of-action--8e2e2d2b-17d4-4cbf-938f-98ee46b3cd3f",
     "created_by_ref": "identity--311b2d2d-f010-4473-83ec-1edf84858f4c",
     "created": "2016-04-06T20:03:48.000Z",
diff --git a/stix2/v21/sdo.py b/stix2/v21/sdo.py
index 59ef168..12a83bd 100644
--- a/stix2/v21/sdo.py
+++ b/stix2/v21/sdo.py
@@ -98,8 +98,9 @@ class CourseOfAction(STIXDomainObject):
     _type = 'course-of-action'
     _properties = OrderedDict([
         ('type', TypeProperty(_type)),
-        ('id', IDProperty(_type, spec_version='2.0')),
-        ('created_by_ref', ReferenceProperty(valid_types='identity', spec_version='2.0')),
+        ('spec_version', StringProperty(fixed='2.1')),
+        ('id', IDProperty(_type, spec_version='2.1')),
+        ('created_by_ref', ReferenceProperty(valid_types='identity', spec_version='2.1')),
         ('created', TimestampProperty(default=lambda: NOW, precision='millisecond')),
         ('modified', TimestampProperty(default=lambda: NOW, precision='millisecond')),
         ('name', StringProperty(required=True)),
@@ -107,7 +108,7 @@ class CourseOfAction(STIXDomainObject):
         ('revoked', BooleanProperty(default=lambda: False)),
         ('labels', ListProperty(StringProperty)),
         ('external_references', ListProperty(ExternalReference)),
-        ('object_marking_refs', ListProperty(ReferenceProperty(valid_types='marking-definition', spec_version='2.0'))),
+        ('object_marking_refs', ListProperty(ReferenceProperty(valid_types='marking-definition', spec_version='2.1'))),
         ('granular_markings', ListProperty(GranularMarking)),
     ])