diff --git a/openpgp/clearsign/clearsign.go b/openpgp/clearsign/clearsign.go
index 6454d22..def4cab 100644
--- a/openpgp/clearsign/clearsign.go
+++ b/openpgp/clearsign/clearsign.go
@@ -118,6 +118,10 @@ func Decode(data []byte) (b *Block, rest []byte) {
 		start := rest
 
 		line, rest = getLine(rest)
+		if len(line) == 0 && len(rest) == 0 {
+			// No armored data was found, so this isn't a complete message.
+			return nil, data
+		}
 		if bytes.Equal(line, endText) {
 			// Back up to the start of the line because armor expects to see the
 			// header line.
diff --git a/openpgp/clearsign/clearsign_test.go b/openpgp/clearsign/clearsign_test.go
index 406377c..2c09480 100644
--- a/openpgp/clearsign/clearsign_test.go
+++ b/openpgp/clearsign/clearsign_test.go
@@ -44,6 +44,12 @@ func TestParse(t *testing.T) {
 	testParse(t, clearsignInput2, "\r\n\r\n(This message has a couple of blank lines at the start and end.)\r\n\r\n", "\n\n(This message has a couple of blank lines at the start and end.)\n\n\n")
 }
 
+func TestParseInvalid(t *testing.T) {
+	if b, _ := Decode(clearsignInput3); b != nil {
+		t.Fatal("decoded a bad clearsigned message without any error")
+	}
+}
+
 func TestParseWithNoNewlineAtEnd(t *testing.T) {
 	input := clearsignInput
 	input = input[:len(input)-len("trailing")-1]
@@ -161,6 +167,13 @@ qZg6BaTvOxepqOxnhVU=
 
 trailing`)
 
+var clearsignInput3 = []byte(`
+-----BEGIN PGP SIGNED MESSAGE-----
+Hash: SHA256
+
+(This message was truncated.)
+`)
+
 var signingKey = `-----BEGIN PGP PRIVATE KEY BLOCK-----
 Version: GnuPG v1.4.10 (GNU/Linux)