diff --git a/DepotDownloader/ContentDownloader.cs b/DepotDownloader/ContentDownloader.cs
index 0015ee95..f072a63e 100644
--- a/DepotDownloader/ContentDownloader.cs
+++ b/DepotDownloader/ContentDownloader.cs
@@ -583,8 +583,30 @@ namespace DepotDownloader
                 if ( lastManifestId != INVALID_MANIFEST_ID )
                 {
                     var oldManifestFileName = Path.Combine( configDir, string.Format( "{0}.bin", lastManifestId ) );
-                    if ( File.Exists( oldManifestFileName ) )
-                        oldProtoManifest = ProtoManifest.LoadFromFile( oldManifestFileName );
+
+                    if (File.Exists(oldManifestFileName))
+                    {
+                        byte[] expectedChecksum, currentChecksum;
+
+                        try
+                        {
+                            expectedChecksum = File.ReadAllBytes(oldManifestFileName + ".sha");
+                        }
+                        catch (IOException)
+                        {
+                            expectedChecksum = null;
+                        }
+
+                        oldProtoManifest = ProtoManifest.LoadFromFile(oldManifestFileName, out currentChecksum);
+
+                        if (expectedChecksum == null || !expectedChecksum.SequenceEqual(currentChecksum))
+                        {
+                            // We only have to show this warning if the old manifest ID was different
+                            if (lastManifestId != depot.manifestId)
+                                Console.WriteLine("Manifest {0} on disk did not match the expected checksum.", lastManifestId);
+                            oldProtoManifest = null;
+                        }
+                    }
                 }
 
                 if ( lastManifestId == depot.manifestId && oldProtoManifest != null )
@@ -597,7 +619,24 @@ namespace DepotDownloader
                     var newManifestFileName = Path.Combine( configDir, string.Format( "{0}.bin", depot.manifestId ) );
                     if ( newManifestFileName != null )
                     {
-                        newProtoManifest = ProtoManifest.LoadFromFile( newManifestFileName );
+                        byte[] expectedChecksum, currentChecksum;
+
+                        try
+                        {
+                            expectedChecksum = File.ReadAllBytes(newManifestFileName + ".sha");
+                        }
+                        catch (IOException)
+                        {
+                            expectedChecksum = null;
+                        }
+
+                        newProtoManifest = ProtoManifest.LoadFromFile(newManifestFileName, out currentChecksum);
+
+                        if (expectedChecksum == null || !expectedChecksum.SequenceEqual(currentChecksum))
+                        {
+                            Console.WriteLine("Manifest {0} on disk did not match the expected checksum.", depot.manifestId);
+                            newProtoManifest = null;
+                        }
                     }
 
                     if ( newProtoManifest != null )
@@ -656,8 +695,11 @@ namespace DepotDownloader
                             return;
                         }
 
+                        byte[] checksum;
+
                         newProtoManifest = new ProtoManifest( depotManifest, depot.manifestId );
-                        newProtoManifest.SaveToFile( newManifestFileName );
+                        newProtoManifest.SaveToFile( newManifestFileName, out checksum );
+                        File.WriteAllBytes( newManifestFileName + ".sha", checksum );
 
                         Console.WriteLine( " Done!" );
                     }
diff --git a/DepotDownloader/ProtoManifest.cs b/DepotDownloader/ProtoManifest.cs
index 6a80da47..7c1c086e 100644
--- a/DepotDownloader/ProtoManifest.cs
+++ b/DepotDownloader/ProtoManifest.cs
@@ -117,21 +117,42 @@ namespace DepotDownloader
         [ProtoMember(2)]
         public ulong ID { get; private set; }
 
-        public static ProtoManifest LoadFromFile(string filename)
+        public static ProtoManifest LoadFromFile(string filename, out byte[] checksum)
         {
             if (!File.Exists(filename))
+            {
+                checksum = null;
                 return null;
+            }
+
+            using (MemoryStream ms = new MemoryStream())
+            {
+                using (FileStream fs = File.Open(filename, FileMode.Open))
+                using (DeflateStream ds = new DeflateStream(fs, CompressionMode.Decompress))
+                    ds.CopyTo(ms);
+
+                checksum = Util.SHAHash(ms.ToArray());
 
-            using (FileStream fs = File.Open(filename, FileMode.Open))
-            using (DeflateStream ds = new DeflateStream(fs, CompressionMode.Decompress))
-                return ProtoBuf.Serializer.Deserialize<ProtoManifest>(ds);
+                ms.Seek(0, SeekOrigin.Begin);
+                return ProtoBuf.Serializer.Deserialize<ProtoManifest>(ms);
+            }
         }
 
-        public void SaveToFile(string filename)
+        public void SaveToFile(string filename, out byte[] checksum)
         {
-            using (FileStream fs = File.Open(filename, FileMode.Create))
-            using (DeflateStream ds = new DeflateStream(fs, CompressionMode.Compress))
-                ProtoBuf.Serializer.Serialize<ProtoManifest>(ds, this);
+            
+            using (MemoryStream ms = new MemoryStream())
+            {
+                ProtoBuf.Serializer.Serialize<ProtoManifest>(ms, this);
+
+                checksum = Util.SHAHash(ms.ToArray());
+
+                ms.Seek(0, SeekOrigin.Begin);
+
+                using (FileStream fs = File.Open(filename, FileMode.Create))
+                using (DeflateStream ds = new DeflateStream(fs, CompressionMode.Compress))
+                    ms.CopyTo(ds);
+            }
         }
     }
 }