diff --git a/peyotls.cabal b/peyotls.cabal
--- a/peyotls.cabal
+++ b/peyotls.cabal
@@ -2,7 +2,7 @@
 cabal-version:	>= 1.8
 
 name:		peyotls
-version:	0.0.0.3
+version:	0.0.0.4
 stability:	Experimental
 author:		Yoshikuni Jujo <PAF01143@nifty.ne.jp>
 maintainer:	Yoshikuni Jujo <PAF01143@nifty.ne.jp>
@@ -272,7 +272,7 @@
 source-repository	this
     type:	git
     location:	git://github.com/YoshikuniJujo/peyotls.git
-    tag:	peyotls-0.0.0.3
+    tag:	peyotls-0.0.0.4
 
 library
     hs-source-dirs:	src
diff --git a/src/Network/PeyoTLS/Client.hs b/src/Network/PeyoTLS/Client.hs
--- a/src/Network/PeyoTLS/Client.hs
+++ b/src/Network/PeyoTLS/Client.hs
@@ -158,11 +158,12 @@
 		Sha1 -> (SHA1.hash, ASN1.OID [1, 3, 14, 3, 2, 26])
 		Sha256 -> (SHA256.hash, ASN1.OID [2, 16, 840, 1, 101, 3, 4, 2, 1])
 		_ -> error "not implemented"
-	Right [ASN1.Start ASN1.Sequence,
-		ASN1.Start ASN1.Sequence, oid, ASN1.Null, ASN1.End ASN1.Sequence,
-		ASN1.OctetString o, ASN1.End ASN1.Sequence ] =
-		ASN1.decodeASN1' ASN1.DER . BS.tail . BS.dropWhile (== 255) .
-			BS.drop 2 $ RSA.ep pk sn in
+	(o, oid) = case ASN1.decodeASN1' ASN1.DER . BS.tail
+		. BS.dropWhile (== 255) . BS.drop 2 $ RSA.ep pk sn of
+		Right [ASN1.Start ASN1.Sequence,
+			ASN1.Start ASN1.Sequence, oid_, ASN1.Null, ASN1.End ASN1.Sequence,
+			ASN1.OctetString o_, ASN1.End ASN1.Sequence ] -> (o_, oid_)
+		e -> error $ show e in
 	oid == oid0 && o == hs m
 
 instance Verify ECDSA.PublicKey where