diff --git a/options_test.go b/options_test.go
new file mode 100644
index 0000000..39421c8
--- /dev/null
+++ b/options_test.go
@@ -0,0 +1,23 @@
+package astra
+
+import "testing"
+
+var optionSets = [][]Option{
+	{
+		IgnoreVariables, IgnoreMethods,
+	},
+	{
+		IgnoreFunctions, IgnoreInterfaces, IgnoreMethods, IgnoreConstants,
+	},
+}
+
+func TestOptions(t *testing.T) {
+	for _, s := range optionSets {
+		concated := concatOptions(s)
+		for i := range s {
+			if !concated.check(s[i]) {
+				t.Error(concated, s[i])
+			}
+		}
+	}
+}
diff --git a/parser.go b/parser.go
index 341804f..1b1c42f 100644
--- a/parser.go
+++ b/parser.go
@@ -23,8 +23,8 @@ var (
 type Option uint
 
 const (
-	IgnoreComments Option = 1
-	IgnoreStructs  Option = iota * 2
+	IgnoreComments Option = 1 << iota
+	IgnoreStructs
 	IgnoreInterfaces
 	IgnoreFunctions
 	IgnoreMethods