diff --git a/Compression.BSA.Test/BSATests.cs b/Compression.BSA.Test/BSATests.cs
index 51a0bbb5..7e61777c 100644
--- a/Compression.BSA.Test/BSATests.cs
+++ b/Compression.BSA.Test/BSATests.cs
@@ -99,6 +99,7 @@ namespace Compression.BSA.Test
 
             TestContext.WriteLine($"Reading {bsa}");
             string tempFile = Path.Combine("tmp.bsa");
+            var size = File.GetSize(bsa);
             using (var a = BSADispatch.OpenRead(bsa))
             {
                 await a.Files.PMap(Queue, file =>
@@ -120,7 +121,7 @@ namespace Compression.BSA.Test
 
                 Console.WriteLine($"Building {bsa}");
 
-                using (var w = ViaJson(a.State).MakeBuilder())
+                using (var w = ViaJson(a.State).MakeBuilder(size))
                 {
                     var streams = await a.Files.PMap(Queue, file =>
                     {
diff --git a/Compression.BSA/BA2Builder.cs b/Compression.BSA/BA2Builder.cs
index 7b77e54a..a7c173ce 100644
--- a/Compression.BSA/BA2Builder.cs
+++ b/Compression.BSA/BA2Builder.cs
@@ -27,10 +27,10 @@ namespace Compression.BSA
         private List<IFileBuilder> _entries = new List<IFileBuilder>();
         private DiskSlabAllocator _slab;
 
-        public BA2Builder(BA2StateObject state)
+        public BA2Builder(BA2StateObject state, long size)
         {
             _state = state;
-            _slab = new DiskSlabAllocator();
+            _slab = new DiskSlabAllocator(size);
         }
         
         public void Dispose()
diff --git a/Compression.BSA/BA2Reader.cs b/Compression.BSA/BA2Reader.cs
index 1f00f7ef..c5a1d055 100644
--- a/Compression.BSA/BA2Reader.cs
+++ b/Compression.BSA/BA2Reader.cs
@@ -125,9 +125,9 @@ namespace Compression.BSA
         public EntryType Type { get; set; }
         public string HeaderMagic { get; set; }
         public uint Version { get; set; }
-        public override IBSABuilder MakeBuilder()
+        public override IBSABuilder MakeBuilder(long size)
         {
-            return new BA2Builder(this);
+            return new BA2Builder(this, size);
         }
     }
 
diff --git a/Compression.BSA/BSABuilder.cs b/Compression.BSA/BSABuilder.cs
index 628a21df..fa434990 100644
--- a/Compression.BSA/BSABuilder.cs
+++ b/Compression.BSA/BSABuilder.cs
@@ -25,14 +25,14 @@ namespace Compression.BSA
         internal uint _version;
         internal DiskSlabAllocator _slab;
 
-        public BSABuilder()
+        public BSABuilder(long size)
         {
             _fileId = Encoding.ASCII.GetBytes("BSA\0");
             _offset = 0x24;
-            _slab = new DiskSlabAllocator();
+            _slab = new DiskSlabAllocator(size);
         }
 
-        public BSABuilder(BSAStateObject bsaStateObject) : this()
+        public BSABuilder(BSAStateObject bsaStateObject, long size) : this(size)
         {
             _version = bsaStateObject.Version;
             _fileFlags = bsaStateObject.FileFlags;
diff --git a/Compression.BSA/BSAReader.cs b/Compression.BSA/BSAReader.cs
index de92c4d6..5d239091 100644
--- a/Compression.BSA/BSAReader.cs
+++ b/Compression.BSA/BSAReader.cs
@@ -163,9 +163,9 @@ namespace Compression.BSA
 
         }
 
-        public override IBSABuilder MakeBuilder()
+        public override IBSABuilder MakeBuilder(long size)
         {
-            return new BSABuilder(this);
+            return new BSABuilder(this, size);
         }
 
         public string Magic { get; set; }
diff --git a/Compression.BSA/IBSAReader.cs b/Compression.BSA/IBSAReader.cs
index 4bcfc23c..ddec769a 100644
--- a/Compression.BSA/IBSAReader.cs
+++ b/Compression.BSA/IBSAReader.cs
@@ -22,7 +22,7 @@ namespace Compression.BSA
 
     public class ArchiveStateObject
     {
-        public virtual IBSABuilder MakeBuilder()
+        public virtual IBSABuilder MakeBuilder(long size)
         {
             throw new NotImplementedException();
         }
diff --git a/Compression.BSA/TES3Reader.cs b/Compression.BSA/TES3Reader.cs
index 28ff9a64..11462a95 100644
--- a/Compression.BSA/TES3Reader.cs
+++ b/Compression.BSA/TES3Reader.cs
@@ -87,7 +87,7 @@ namespace Compression.BSA
         public uint HashOffset { get; set; }
         public uint VersionNumber { get; set; }
 
-        public override IBSABuilder MakeBuilder()
+        public override IBSABuilder MakeBuilder(long size)
         {
             return new TES3Builder(this);
         }
diff --git a/Wabbajack.Common/Util/DiskSlabAllocator.cs b/Wabbajack.Common/Util/DiskSlabAllocator.cs
index effdee3b..4e108e5e 100644
--- a/Wabbajack.Common/Util/DiskSlabAllocator.cs
+++ b/Wabbajack.Common/Util/DiskSlabAllocator.cs
@@ -14,11 +14,13 @@ namespace Wabbajack.Common
         private MemoryMappedFile _mmap;
         private long _head = 0;
         private string _name;
+        private FileStream _fileStream;
 
-        public DiskSlabAllocator()
+        public DiskSlabAllocator(long size)
         {
-            _name = Guid.NewGuid().ToString();
-            _mmap = MemoryMappedFile.CreateNew(null, (long)1 << 34);
+            _file = new TempFile();
+            _fileStream = _file.File.Open(FileMode.Create, FileAccess.ReadWrite);
+            _mmap = MemoryMappedFile.CreateFromFile(_fileStream, null, size, MemoryMappedFileAccess.ReadWrite, HandleInheritability.None, false);
         }
 
         public Stream Allocate(long size)
@@ -34,6 +36,8 @@ namespace Wabbajack.Common
         public void Dispose()
         {
             _mmap?.Dispose();
+            _fileStream?.Dispose();
+            _file?.Dispose();
         }
     }
 }
diff --git a/Wabbajack.Lib/MO2Installer.cs b/Wabbajack.Lib/MO2Installer.cs
index 6a7b23f2..acb2238b 100644
--- a/Wabbajack.Lib/MO2Installer.cs
+++ b/Wabbajack.Lib/MO2Installer.cs
@@ -1,4 +1,5 @@
 using System;
+using System.ComponentModel.DataAnnotations;
 using System.Globalization;
 using System.IO;
 using System.Linq;
@@ -237,7 +238,9 @@ namespace Wabbajack.Lib
                 Status($"Building {bsa.To}");
                 var sourceDir = Path.Combine(OutputFolder, Consts.BSACreationDir, bsa.TempID);
 
-                using (var a = bsa.State.MakeBuilder())
+                var bsaSize = bsa.FileStates.Select(state => File.GetSize(Path.Combine(sourceDir, state.Path))).Sum();
+
+                using (var a = bsa.State.MakeBuilder(bsaSize))
                 {
                     var streams = await bsa.FileStates.PMap(Queue, state =>
                     {