diff --git a/ir.py b/ir.py
index cf7d2ba..809f555 100644
--- a/ir.py
+++ b/ir.py
@@ -292,7 +292,7 @@ class Switch:
 	def subst(self, expression: Expression, variable: str) -> Expression:
 		return Switch(
 			{i: e.subst(expression, variable) for i, e in self.branches.items()},
-			self.fallback,
+			self.fallback.subst(expression, variable),
 			self.switching_on.subst(expression, variable))
 
 	def is_value(self) -> bool: