diff --git a/resource.go b/resource.go
index cdf8401..b2590be 100644
--- a/resource.go
+++ b/resource.go
@@ -34,7 +34,7 @@ const (
 )
 
 const (
-	IsExpr = 1 << iota
+	IsExpr byte = 1 << iota
 	IsOmitempty
 	Ignored
 )