diff --git a/scipost/views.py b/scipost/views.py
index b58d42b0cc5b6b1b82cb6c1fbe27c0d33d3c5a09..68344390f9acae199e321c5947d37b0be4811a65 100644
--- a/scipost/views.py
+++ b/scipost/views.py
@@ -268,15 +268,18 @@ def vet_registration_request_ack(request, contributor_id):
             contributor.save()
             group = Group.objects.get(name='Registered Contributors')
             contributor.user.groups.add(group)
+
             # Verify if there is a pending refereeing invitation
-            pending_ref_inv_exists = True
-            try:
-                pending_ref_inv = RefereeInvitation.objects.get(
-                    invitation_key=contributor.invitation_key, cancelled=False)
-                pending_ref_inv.referee = contributor
-                pending_ref_inv.save()
-            except RefereeInvitation.DoesNotExist:
-                pending_ref_inv_exists = False
+            pending_ref_inv_exists = False
+            if contributor.invitation_key:
+                try:
+                    pending_ref_inv = RefereeInvitation.objects.get(
+                        invitation_key=contributor.invitation_key, cancelled=False)
+                    pending_ref_inv.referee = contributor
+                    pending_ref_inv.save()
+                    pending_ref_inv_exists = True
+                except RefereeInvitation.DoesNotExist:
+                    pending_ref_inv_exists = False
 
             email_text = (
                 'Dear ' + contributor.get_title_display() + ' ' + contributor.user.last_name +