diff --git a/age/src/format.rs b/age/src/format.rs
index ac83331..7b5bb31 100644
--- a/age/src/format.rs
+++ b/age/src/format.rs
@@ -298,7 +298,7 @@ mod write {
     pub(super) fn header<'a, W: 'a + Write>(h: &'a Header) -> impl SerializeFn<W> + 'a {
         move |w: WriteContext<W>| match h {
             Header::V1(v1) => header_v1(v1)(w),
-            Header::Unknown(version) => panic!("Cannot write header for version {}", version),
+            Header::Unknown(version) => tuple((slice(AGE_MAGIC), slice(version), string("\n")))(w),
         }
     }
 }
diff --git a/age/src/lib.rs b/age/src/lib.rs
index d2d3d0e..d306bac 100644
--- a/age/src/lib.rs
+++ b/age/src/lib.rs
@@ -127,12 +127,8 @@ pub mod cli_common;
 #[cfg(fuzzing)]
 pub fn fuzz_header(data: &[u8]) {
     if let Ok(header) = format::Header::read(data) {
-        if let format::Header::Unknown(_) = header {
-            // Unknown headers cause panics on write.
-        } else {
-            let mut buf = Vec::with_capacity(data.len());
-            header.write(&mut buf).expect("can write header");
-            assert_eq!(&buf[..], &data[..buf.len()]);
-        }
+        let mut buf = Vec::with_capacity(data.len());
+        header.write(&mut buf).expect("can write header");
+        assert_eq!(&buf[..], &data[..buf.len()]);
     }
 }