diff --git a/submissions/models.py b/submissions/models.py
index 001ad68f23715b81bb13777e19f6eb7c814a3f03..5936bd4ca05d903e27bdaf347fcfd24e0c7fbf0f 100644
--- a/submissions/models.py
+++ b/submissions/models.py
@@ -501,7 +501,8 @@ class Report(SubmissionRelatedObjectMixin, models.Model):
     def save(self, *args, **kwargs):
         """Update report number before saving on creation."""
         if not self.report_nr:
-            self.report_nr = self.submission.reports.count() + 1
+            self.report_nr = self.submission.reports.aggregate(
+                models.Max('report_nr')).get('report_nr__max', 0) + 1
         return super().save(*args, **kwargs)
 
     def get_absolute_url(self):