diff --git a/armor/armor.go b/armor/armor.go
index 4ba9473..c6b5fb0 100644
--- a/armor/armor.go
+++ b/armor/armor.go
@@ -146,6 +146,10 @@ func (r *armoredReader) Read(p []byte) (int, error) {
 	if len(line) > format.ColumnsPerLine {
 		return 0, r.setErr(errors.New("column limit exceeded"))
 	}
+	// Reject newline characters ignored by base64.Decode.
+	if bytes.ContainsAny(line, "\n\r") {
+		return 0, r.setErr(errors.New("unexpected newline character"))
+	}
 	r.unread = r.buf[:]
 	n, err := base64.StdEncoding.Strict().Decode(r.unread, line)
 	if err != nil {
diff --git a/go.mod b/go.mod
index 316cb19..ccfee06 100644
--- a/go.mod
+++ b/go.mod
@@ -16,7 +16,7 @@ require (
 
 // Test dependencies.
 require (
-	c2sp.org/CCTV/age v0.0.0-20260605191406-1e3d2860d46e
+	c2sp.org/CCTV/age v0.0.0-20260829155415-4448f2097b2d
 	github.com/rogpeppe/go-internal v1.16.0
 	golang.org/x/tools v0.49.0 // indirect
 )
diff --git a/go.sum b/go.sum
index 361ab4a..c1944d2 100644
--- a/go.sum
+++ b/go.sum
@@ -1,5 +1,5 @@
-c2sp.org/CCTV/age v0.0.0-20260605191406-1e3d2860d46e h1:N9DpijOhcuCLIlgcX/6qhBQeMQIlBxsVQITjbpJaBso=
-c2sp.org/CCTV/age v0.0.0-20260605191406-1e3d2860d46e/go.mod h1:SrHC2C7r5GkDk8R+NFVzYy/sdj0Ypg9htaPXQq5Cqeo=
+c2sp.org/CCTV/age v0.0.0-20260829155415-4448f2097b2d h1:Blprhc2SbChNZtWcU+BLTM4YdoqYAS9V7cJgOwJKyAs=
+c2sp.org/CCTV/age v0.0.0-20260829155415-4448f2097b2d/go.mod h1:SrHC2C7r5GkDk8R+NFVzYy/sdj0Ypg9htaPXQq5Cqeo=
 filippo.io/edwards25519 v1.2.0 h1:crnVqOiS4jqYleHd9vaKZ+HKtHfllngJIiOpNpoJsjo=
 filippo.io/edwards25519 v1.2.0/go.mod h1:xzAOLCNug/yB62zG1bQ8uziwrIqIuxhctzJT18Q77mc=
 filippo.io/hpke v0.4.0 h1:p575VVQ6ted4pL+it6M00V/f2qTZITO0zgmdKCkd5+A=