diff --git a/docs/sophia_syntax.md b/docs/sophia_syntax.md
index a49eb0e..9a4b748 100644
--- a/docs/sophia_syntax.md
+++ b/docs/sophia_syntax.md
@@ -182,6 +182,10 @@ LetDef ::= Id Args [':' Type] '=' Block(Stmt)   // Function definition
          | Pattern '=' Block(Stmt)              // Value definition
 
 Case    ::= Pattern '=>' Block(Stmt)
+          | Pattern Block(GuardedCase)
+
+GuardedCase ::= '|' Sep1(Expr, ',') '=>' Block(Stmt)
+
 Pattern ::= Expr
 ```