diff --git a/alyx/alyx/base.py b/alyx/alyx/base.py
index 83444ffc..bd971157 100644
--- a/alyx/alyx/base.py
+++ b/alyx/alyx/base.py
@@ -6,7 +6,6 @@
 import sys
 import pytz
 import uuid
-from collections import OrderedDict
 import one.alf.spec
 from datetime import datetime
 import traceback
@@ -445,7 +444,7 @@ def ar(self, r, code=200):
         """
         self.assertTrue(r.status_code == code, r.data)
         pkeys = {'count', 'next', 'previous', 'results'}
-        if isinstance(r.data, OrderedDict) and set(r.data.keys()) == pkeys:
+        if isinstance(r.data, dict) and set(r.data.keys()) == pkeys:
             return r.data['results']
         else:
             return r.data
diff --git a/alyx/experiments/models.py b/alyx/experiments/models.py
index c0836e22..db42de59 100644
--- a/alyx/experiments/models.py
+++ b/alyx/experiments/models.py
@@ -181,8 +181,12 @@ class TrajectoryEstimate(models.Model):
 
     class Meta:
         constraints = [
+            models.UniqueConstraint(fields=['provenance', 'chronic_insertion'],
+                                    condition=models.Q(probe_insertion__isnull=True),
+                                    name='unique_trajectory_per_chronic_provenance'),
             models.UniqueConstraint(fields=['provenance', 'probe_insertion'],
-                                    name='unique_trajectory_per_provenance')
+                                    condition=models.Q(probe_insertion__isnull=False),
+                                    name='unique_trajectory_per_provenance'),
         ]
 
     def __str__(self):
diff --git a/alyx/experiments/serializers.py b/alyx/experiments/serializers.py
index 0c2c64ec..92ad06a8 100644
--- a/alyx/experiments/serializers.py
+++ b/alyx/experiments/serializers.py
@@ -27,9 +27,10 @@ class Meta:
 
 class TrajectoryEstimateSerializer(serializers.ModelSerializer):
     probe_insertion = serializers.SlugRelatedField(
-        read_only=False, required=False, slug_field='id', many=False,
+        read_only=False, required=False, slug_field='id', many=False, allow_null=True,
         queryset=ProbeInsertion.objects.all(),
     )
+
     x = serializers.FloatField(required=True, allow_null=True)
     y = serializers.FloatField(required=True, allow_null=True)
     z = serializers.FloatField(required=False, allow_null=True)
@@ -45,6 +46,15 @@ class TrajectoryEstimateSerializer(serializers.ModelSerializer):
         queryset=CoordinateSystem.objects.all(),
     )
 
+    def to_internal_value(self, data):
+        if data.get('chronic_insertion', None) is None:
+            data['chronic_insertion'] = None
+
+        if data.get('probe_insertion', None) is None:
+            data['probe_insertion'] = None
+
+        return super(TrajectoryEstimateSerializer, self).to_internal_value(data)
+
     class Meta:
         model = TrajectoryEstimate
         fields = '__all__'
diff --git a/alyx/experiments/tests_rest.py b/alyx/experiments/tests_rest.py
index a717d86f..c2138d1e 100644
--- a/alyx/experiments/tests_rest.py
+++ b/alyx/experiments/tests_rest.py
@@ -465,7 +465,7 @@ def test_create_list_delete_fov(self):
         url = reverse('fovlocation-list')
         with transaction.atomic():
             response = self.post(url, loc_dict)
-            self.ar(response, 500)
+            self.assertIn(response.status_code, (400, 500))  # In later versions status code is 400
 
         url = reverse('fieldsofview-list')
         # FOV location containing atlas ID 9 should no longer be default provenance and therefore