diff --git a/store/search_test.go b/store/search_test.go
index 995bb05..c573e4c 100644
--- a/store/search_test.go
+++ b/store/search_test.go
@@ -13,7 +13,7 @@ func TestSubjectMatch(t *testing.T) {
 	originalSubject := `テストテキスト Abc 123...`
 	asciiSubject := "test text Abc 123..."
 
-	encodedSubjectUTF8 := `=?UTF-8?B?44OG44K544OI44OG44Kt44K544OIIEFiYyAxMjMuLi4=?=`
+	encodedSubjectUTF8 := `=?UTF-8?b?44OG44K544OI44OG44Kt44K544OIIEFiYyAxMjMuLi4=?=`
 	encodedSubjectISO2022 := `=?iso-2022-jp?B?GyRCJUYlOSVIJUYlLSU5JUgbKEIgQWJjIDEyMy4uLg==?=`
 	encodedSubjectUTF8 = encodedSubjectUTF8 + " \n " + encodedSubjectUTF8
 	encodedSubjectISO2022 = encodedSubjectISO2022 + " \n " + encodedSubjectISO2022