diff --git a/src/cmd/compile/internal/ir/expr.go b/src/cmd/compile/internal/ir/expr.go
index 0639c3b620..39659c45c0 100644
--- a/src/cmd/compile/internal/ir/expr.go
+++ b/src/cmd/compile/internal/ir/expr.go
@@ -145,7 +145,7 @@ func (n *BinaryExpr) SetOp(op Op) {
 }
 
 // A CallUse records how the result of the call is used:
-type CallUse int
+type CallUse byte
 
 const (
 	_ CallUse = iota