diff --git a/contentcuration/contentcuration/tests/viewsets/test_contentnode.py b/contentcuration/contentcuration/tests/viewsets/test_contentnode.py
index 48c5ead8ac..4402db855a 100644
--- a/contentcuration/contentcuration/tests/viewsets/test_contentnode.py
+++ b/contentcuration/contentcuration/tests/viewsets/test_contentnode.py
@@ -36,7 +36,6 @@
 from contentcuration.viewsets.sync.constants import CONTENTNODE_PREREQUISITE
 from contentcuration.viewsets.sync.constants import UPDATED
 
-
 nested_subjects = [subject for subject in SUBJECTSLIST if "." in subject]
 
 
@@ -816,6 +815,47 @@ def test_update_contentnode_update_options_completion_criteria_threshold_only(se
         self.assertEqual(c.extra_fields["options"]["completion_criteria"]["model"], completion_criteria.TIME)
         self.assertEqual(c.extra_fields["options"]["completion_criteria"]["threshold"], 10)
 
+    def test_update_completion_criteria_model_to_determined_by_resource_edge_case(self):
+        metadata = self.contentnode_db_metadata
+        metadata["kind_id"] = content_kinds.HTML5
+        metadata["extra_fields"] = {
+            "options": {
+                "completion_criteria": {
+                    "model": completion_criteria.REFERENCE,
+                    "threshold": None,
+                    "learner_managed": False
+                }
+            }
+        }
+        contentnode = models.ContentNode.objects.create(**metadata)
+
+        response = self.sync_changes(
+                [
+                    generate_update_event(
+                        contentnode.id,
+                        CONTENTNODE,
+                        {
+                            "complete": True,
+                            "extra_fields.options.completion_criteria.threshold": 600,
+                            "extra_fields.options.completion_criteria.model": completion_criteria.APPROX_TIME
+                        },
+                        channel_id=self.channel.id
+                    ),
+                    generate_update_event(
+                        contentnode.id,
+                        CONTENTNODE,
+                        {
+                            "extra_fields.options.completion_criteria.model": completion_criteria.DETERMINED_BY_RESOURCE
+                        },
+                        channel_id=self.channel.id
+                    )
+                ],
+        )
+        self.assertEqual(len(response.data["errors"]), 0)
+        updated_contentnode = models.ContentNode.objects.get(id=contentnode.id)
+        self.assertEqual(updated_contentnode.extra_fields["options"]["completion_criteria"]["model"], completion_criteria.DETERMINED_BY_RESOURCE)
+        self.assertNotIn("threshold", updated_contentnode.extra_fields["options"]["completion_criteria"])
+
     def test_update_contentnode_update_options_invalid_completion_criteria(self):
         metadata = self.contentnode_db_metadata
         metadata["extra_fields"] = {
diff --git a/contentcuration/contentcuration/utils/nodes.py b/contentcuration/contentcuration/utils/nodes.py
index 61491305d1..c84467a5cc 100644
--- a/contentcuration/contentcuration/utils/nodes.py
+++ b/contentcuration/contentcuration/utils/nodes.py
@@ -453,3 +453,11 @@ def migrate_extra_fields(extra_fields):
             "model": completion_criteria.MASTERY,
         }
     return extra_fields
+
+
+def validate_and_conform_to_schema_threshold_none(completion_criteria_validated):
+    model = completion_criteria_validated.get("model", {})
+    if model in ["reference", "determined_by_resource"]:
+        if "threshold" not in completion_criteria_validated or completion_criteria_validated["threshold"] is not None:
+            completion_criteria_validated["threshold"] = None
+    return completion_criteria_validated
diff --git a/contentcuration/contentcuration/viewsets/contentnode.py b/contentcuration/contentcuration/viewsets/contentnode.py
index b15b717860..35889bbfcb 100644
--- a/contentcuration/contentcuration/viewsets/contentnode.py
+++ b/contentcuration/contentcuration/viewsets/contentnode.py
@@ -58,6 +58,7 @@
 from contentcuration.utils.nodes import calculate_resource_size
 from contentcuration.utils.nodes import migrate_extra_fields
 from contentcuration.utils.pagination import ValuesViewsetCursorPagination
+from contentcuration.utils.nodes import validate_and_conform_to_schema_threshold_none
 from contentcuration.viewsets.base import BulkListSerializer
 from contentcuration.viewsets.base import BulkModelSerializer
 from contentcuration.viewsets.base import BulkUpdateMixin
@@ -281,6 +282,10 @@ class CompletionCriteriaSerializer(JSONFieldDictSerializer):
     model = CharField()
     learner_managed = BooleanField(required=False, allow_null=True)
 
+    def update(self, instance, validated_data):
+        validated_data = validate_and_conform_to_schema_threshold_none(validated_data)
+        return super(CompletionCriteriaSerializer, self).update(instance, validated_data)
+
 
 class ExtraFieldsOptionsSerializer(JSONFieldDictSerializer):
     modality = ChoiceField(choices=(("QUIZ", "Quiz"),), allow_null=True, required=False)