diff --git a/C#-and-.NET-docs-supplement.md b/C#-and-.NET-docs-supplement.md
index c5e79c0..8f658a3 100644
--- a/C#-and-.NET-docs-supplement.md
+++ b/C#-and-.NET-docs-supplement.md
@@ -64,6 +64,10 @@ see [feature matrix](https://github.com/TASEmulators/BizHawk/wiki/Available-C%23
 
 You can only have 1 `default:` branch (not to be confused with `case default:`), but you can't simply add a guard clause: `case _ when ...:` doesn't work. However, `case var _ when ...:` does.
 
+## `MemoryMarshal.Cast` can't be used with reference types
+
+See [this SO answer](https://stackoverflow.com/a/79146967/7467292). tl;dr: It's possible in .NET Core only.
+
 ## MSBuild `Condition` placement
 
 On (older versions of?) VS, `Condition` is ignored if placed on a property/item. Create a new `<PropertyGroup/>`/`<ItemGroup/>`.