diff --git a/C#-and-.NET-docs-supplement.md b/C#-and-.NET-docs-supplement.md
index db8b33b..f922dda 100644
--- a/C#-and-.NET-docs-supplement.md
+++ b/C#-and-.NET-docs-supplement.md
@@ -11,6 +11,10 @@ To save us repeating our complaints about the lack of proper documentation under
 
 see [feature matrix](https://github.com/TASEmulators/BizHawk/wiki/Available-C%23-and-.NET-features) page
 
+## Guarded `default` in `switch` statements
+
+You can only have 1 `default` branch, but `case _ when ...:` doesn't work. However, `case var _ when ...:` does.
+
 ## MSBuild `Condition` placement
 
 On (older versions of?) VS, `Condition` is ignored if placed on a property. Create a new `<PropertyGroup/>`.