diff --git a/services/Directory/FilterLists.Directory.Domain/Aggregates/FilterLists/FilterList.cs b/services/Directory/FilterLists.Directory.Domain/Aggregates/FilterLists/FilterList.cs
index 5f3cbc71c..fac24bfab 100644
--- a/services/Directory/FilterLists.Directory.Domain/Aggregates/FilterLists/FilterList.cs
+++ b/services/Directory/FilterLists.Directory.Domain/Aggregates/FilterLists/FilterList.cs
@@ -48,6 +48,14 @@ public static FilterList CreatePendingApproval(
             throw new ArgumentException("At lest one view URL is required.", nameof(viewUrls));
         }
 
+        if (urls.GroupBy(u => new { u.SegmentNumber, u.Primariness })
+            .Any(g => g.Count() > 1))
+        {
+            throw new ArgumentException(
+                "The segment number and primariness pair must be unique for each view URL.",
+                nameof(viewUrls));
+        }
+
         var list = new FilterList
         {
             Name = name,
diff --git a/services/Directory/FilterLists.Directory.Domain/Aggregates/FilterLists/FilterListViewUrl.cs b/services/Directory/FilterLists.Directory.Domain/Aggregates/FilterLists/FilterListViewUrl.cs
index 64c89dbf7..f82a90d43 100644
--- a/services/Directory/FilterLists.Directory.Domain/Aggregates/FilterLists/FilterListViewUrl.cs
+++ b/services/Directory/FilterLists.Directory.Domain/Aggregates/FilterLists/FilterListViewUrl.cs
@@ -10,6 +10,20 @@ protected FilterListViewUrl() { }
 
     internal static FilterListViewUrl Create(short segmentNumber, short primariness, Uri url)
     {
+        if (segmentNumber < 1)
+        {
+            throw new ArgumentException(
+                "The segment number must be greater than or equal to 1.",
+                nameof(segmentNumber));
+        }
+
+        if (primariness < 1)
+        {
+            throw new ArgumentException(
+                "The primariness must be greater than or equal to 1.",
+                nameof(segmentNumber));
+        }
+
         return new FilterListViewUrl { SegmentNumber = segmentNumber, Primariness = primariness, Url = url };
     }
 }