diff --git a/milterutil/transformer.go b/milterutil/transformer.go
index f888bce..001ce7c 100644
--- a/milterutil/transformer.go
+++ b/milterutil/transformer.go
@@ -22,7 +22,6 @@ func (t *CrLfToLfTransformer) Transform(dst, src []byte, atEOF bool) (nDst, nSrc
 		if c == lf {
 			if t.prevCR {
 				nSrc++
-				dst[nDst-1] = lf
 				t.prevCR = false
 				continue
 			}
diff --git a/milterutil/transformer_test.go b/milterutil/transformer_test.go
index d598583..2dcb74e 100644
--- a/milterutil/transformer_test.go
+++ b/milterutil/transformer_test.go
@@ -93,6 +93,8 @@ func TestCrLfToLfTransformer(t *testing.T) {
 		{[]string{"\r", "\n"}, "\n"},
 		{[]string{"\r\r", "\n"}, "\n\n"},
 		{[]string{stuffing + "123456\r", "\n"}, stuffing + "123456\n"},
+		// regression https://github.com/d--j/go-milter/pull/20
+		{[]string{"aaaaaaaaaaaaaaaaaaaaaaaa\r\naaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\r\nbbbbbbb"}, "aaaaaaaaaaaaaaaaaaaaaaaa\naaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\nbbbbbbb"},
 	})
 }