diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5438c0d6ce..ce2348372a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -26,6 +26,7 @@ All notable changes to this project will be documented in this file.
 - [GUI] Mod list fixes and improvements (#3883 by: HebaruSan; reviewed: techman83)
 - [Multiple] Multi-game labels (#3885 by: HebaruSan; reviewed: techman83)
 - [Multiple] Alternate mod dirs for validation and manual installs (#3891 by: HebaruSan; reviewed: techman83)
+- [Core] Fix archive.org fallback URLs for versions with spaces (#3899 by: HebaruSan)
 
 ### Internal
 
diff --git a/Core/Net/NetFileCache.cs b/Core/Net/NetFileCache.cs
index 0830a50639..4190552df7 100644
--- a/Core/Net/NetFileCache.cs
+++ b/Core/Net/NetFileCache.cs
@@ -126,10 +126,10 @@ public string GetInProgressFileName(Uri url, string description)
 
         public string GetInProgressFileName(List<Uri> urls, string description)
         {
-            var filenames = urls.Select(url => GetInProgressFileName(NetFileCache.CreateURLHash(url), description))
-                                .ToArray();
-            return filenames.FirstOrDefault(filename => File.Exists(filename))
-                ?? filenames.FirstOrDefault();
+            var filenames = urls?.Select(url => GetInProgressFileName(NetFileCache.CreateURLHash(url), description))
+                                 .ToArray();
+            return filenames?.FirstOrDefault(filename => File.Exists(filename))
+                ?? filenames?.FirstOrDefault();
         }
 
         /// <summary>
diff --git a/Core/Net/NetModuleCache.cs b/Core/Net/NetModuleCache.cs
index 387b905a73..8c0bf0a9c8 100644
--- a/Core/Net/NetModuleCache.cs
+++ b/Core/Net/NetModuleCache.cs
@@ -94,7 +94,9 @@ public void CheckFreeSpace(long bytesToStore)
         }
 
         public string GetInProgressFileName(CkanModule m)
-            => cache.GetInProgressFileName(m.download, m.StandardName());
+            => m.download == null
+                ? null
+                : cache.GetInProgressFileName(m.download, m.StandardName());
 
         private static string DescribeUncachedAvailability(CkanModule m, FileInfo fi)
             => fi.Exists
diff --git a/Core/Types/CkanModule.cs b/Core/Types/CkanModule.cs
index 30c975a526..8e2e13bda7 100644
--- a/Core/Types/CkanModule.cs
+++ b/Core/Types/CkanModule.cs
@@ -784,7 +784,7 @@ public Uri InternetArchiveDownload
         {
             get
             {
-                string verStr = version.ToString().Replace(':', '-');
+                string verStr = version.ToString().Replace(' ', '_').Replace(':', '-');
                 // Some alternate registry repositories don't set download_hash
                 return (download_hash?.sha1 != null && license.All(l => l.Redistributable))
                     ? new Uri(