diff --git a/NHSE.Core/Save/Meta/HorizonSave.cs b/NHSE.Core/Save/Meta/HorizonSave.cs
index 50492e3..b503252 100644
--- a/NHSE.Core/Save/Meta/HorizonSave.cs
+++ b/NHSE.Core/Save/Meta/HorizonSave.cs
@@ -57,5 +57,27 @@ public void ChangeIdentity(byte[] original, byte[] updated)
             foreach (var pair in Players.SelectMany(z => z))
                 pair.Data.ReplaceOccurrences(original, updated);
         }
+
+        public bool ValidateSizes()
+        {
+            var info = Main.Info.GetKnownRevisionIndex();
+            if (info < 0)
+                return false;
+            var sizes = RevisionChecker.SizeInfo[info];
+            if (Main.Data.Length != sizes.Main)
+                return false;
+            foreach (var p in Players)
+            {
+                if (p.Personal.Data.Length != sizes.Personal)
+                    return false;
+                if (p.Photo.Data.Length != sizes.PhotoStudioIsland)
+                    return false;
+                if (p.PostBox.Data.Length != sizes.PostBox)
+                    return false;
+                if (p.Profile.Data.Length != sizes.Profile)
+                    return false;
+            }
+            return true;
+        }
     }
 }
diff --git a/NHSE.WinForms/Main.cs b/NHSE.WinForms/Main.cs
index bb70397..d3944a9 100644
--- a/NHSE.WinForms/Main.cs
+++ b/NHSE.WinForms/Main.cs
@@ -27,7 +27,18 @@ public Main()
                 Open(args[i]);
         }
 
-        private static void Open(HorizonSave file) => new Editor(file).Show();
+        private static void Open(HorizonSave file)
+        {
+            bool sized = file.ValidateSizes();
+            if (!sized)
+            {
+                const string sizeBad = "Save file sizes appear to be incorrect.";
+                if (WinFormsUtil.Prompt(MessageBoxButtons.YesNo, sizeBad, "Continue?") != DialogResult.Yes)
+                    return;
+            }
+
+            new Editor(file).Show();
+        }
 
         private void Main_DragEnter(object sender, DragEventArgs e)
         {