diff --git a/CHANGELOG.md b/CHANGELOG.md
index c3a1c4042..9ad501620 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -36,6 +36,7 @@ All notable changes to this project will be documented in this file.
 - [GUI] Use better console hiding API (#4051 by: HebaruSan)
 - [Core] Trigger progress updates for frozen downloads (#4052 by: HebaruSan)
 - [GUI] Fix NRE on trying to update all when there's nothing to update (#4054 by: HebaruSan)
+- [Core] Tolerate null repo URLs (#4077 by: HebaruSan)
 
 ### Internal
 
diff --git a/Core/Net/NetFileCache.cs b/Core/Net/NetFileCache.cs
index 614fe1e04..98097b979 100644
--- a/Core/Net/NetFileCache.cs
+++ b/Core/Net/NetFileCache.cs
@@ -555,7 +555,7 @@ public static string CreateURLHash(Uri url)
         {
             using (SHA1 sha1 = SHA1.Create())
             {
-                byte[] hash = sha1.ComputeHash(Encoding.UTF8.GetBytes(url.ToString()));
+                byte[] hash = sha1.ComputeHash(Encoding.UTF8.GetBytes(url?.ToString() ?? ""));
 
                 return BitConverter.ToString(hash).Replace("-", "").Substring(0, 8);
             }
diff --git a/Core/Repositories/Repository.cs b/Core/Repositories/Repository.cs
index 8dd85c5f5..6e449599b 100644
--- a/Core/Repositories/Repository.cs
+++ b/Core/Repositories/Repository.cs
@@ -49,7 +49,7 @@ public bool Equals(Repository other)
             => other != null && uri == other.uri;
 
         public override int GetHashCode()
-            => uri.GetHashCode();
+            => uri?.GetHashCode() ?? 0;
 
         public override string ToString()
             => string.Format("{0} ({1}, {2})", name, priority, uri);
diff --git a/Core/Repositories/RepositoryDataManager.cs b/Core/Repositories/RepositoryDataManager.cs
index 3b014e3ed..4e76e8363 100644
--- a/Core/Repositories/RepositoryDataManager.cs
+++ b/Core/Repositories/RepositoryDataManager.cs
@@ -91,7 +91,7 @@ public IEnumerable<AvailableModule> GetAllAvailableModules(IEnumerable<Repositor
         public void Prepopulate(List<Repository> repos, IProgress<int> percentProgress)
         {
             // Look up the sizes of repos that have uncached files
-            var reposAndSizes = repos.Where(r => !repositoriesData.ContainsKey(r))
+            var reposAndSizes = repos.Where(r => r.uri != null && !repositoriesData.ContainsKey(r))
                                      .Select(r => new Tuple<Repository, string>(r, GetRepoDataPath(r)))
                                      .Where(tuple => File.Exists(tuple.Item2))
                                      .Select(tuple => new Tuple<Repository, long>(tuple.Item1,
@@ -140,13 +140,15 @@ public UpdateResult Update(Repository[]       repos,
 
             // Check if any ETags have changed, quit if not
             user.RaiseProgress(Properties.Resources.NetRepoCheckingForUpdates, 0);
-            var toUpdate = repos.DefaultIfEmpty(new Repository("default", game.DefaultRepositoryURL))
+            var toUpdate = repos.DefaultIfEmpty(new Repository($"{game.ShortName}-{Repository.default_ckan_repo_name}",
+                                                               game.DefaultRepositoryURL))
                                 .DistinctBy(r => r.uri)
-                                .Where(r => r.uri.IsFile
-                                            || skipETags
-                                            || (!etags.TryGetValue(r.uri, out string etag)
-                                                || !File.Exists(GetRepoDataPath(r))
-                                                || etag != Net.CurrentETag(r.uri)))
+                                .Where(r => r.uri != null
+                                            && (r.uri.IsFile
+                                                || skipETags
+                                                || (!etags.TryGetValue(r.uri, out string etag)
+                                                    || !File.Exists(GetRepoDataPath(r))
+                                                    || etag != Net.CurrentETag(r.uri))))
                                 .ToArray();
             if (toUpdate.Length < 1)
             {
@@ -300,7 +302,7 @@ private IEnumerable<RepositoryData> GetRepoDatas(IEnumerable<Repository> repos)
             new Dictionary<Repository, RepositoryData>();
 
         private string GetRepoDataPath(Repository repo)
-            => GetRepoDataPath(repo, NetFileCache.CreateURLHash(repo.uri));
+            => GetRepoDataPath(repo, NetFileCache.CreateURLHash(repo?.uri));
 
         private string GetRepoDataPath(Repository repo, string hash)
             => Directory.EnumerateFiles(reposDir)
diff --git a/GUI/Dialogs/SettingsDialog.cs b/GUI/Dialogs/SettingsDialog.cs
index 5cadd1215..dc6dc74a2 100644
--- a/GUI/Dialogs/SettingsDialog.cs
+++ b/GUI/Dialogs/SettingsDialog.cs
@@ -134,7 +134,7 @@ private void RefreshReposListBox(bool saveChanges = true)
                 .OrderBy(r => r.priority)
                 .Select(r => new ListViewItem(new string[]
                     {
-                        r.name, r.uri.ToString(),
+                        r.name, r.uri?.ToString() ?? "",
                     })
                     {
                         Tag = r,