diff --git a/noodles-bam/src/io/reader/header.rs b/noodles-bam/src/io/reader/header.rs
index 0331d14fb..c9fd80508 100644
--- a/noodles-bam/src/io/reader/header.rs
+++ b/noodles-bam/src/io/reader/header.rs
@@ -9,35 +9,49 @@ use noodles_sam::{self as sam, header::ReferenceSequences};
 use self::reference_sequences::read_reference_sequences;
 use crate::MAGIC_NUMBER;
 
-pub(super) fn read_header<R>(reader: &mut R) -> io::Result<sam::Header>
+struct Reader<'r, R> {
+    inner: &'r mut R,
+}
+
+impl<'r, R> Reader<'r, R>
 where
     R: Read,
 {
-    read_magic(reader)?;
+    fn new(inner: &'r mut R) -> Self {
+        Self { inner }
+    }
 
-    let mut header = read_header_inner(reader)?;
-    let reference_sequences = read_reference_sequences(reader)?;
+    fn read_magic_number(&mut self) -> io::Result<[u8; MAGIC_NUMBER.len()]> {
+        let mut buf = [0; MAGIC_NUMBER.len()];
+        self.inner.read_exact(&mut buf)?;
+        Ok(buf)
+    }
 
-    if header.reference_sequences().is_empty() {
-        *header.reference_sequences_mut() = reference_sequences;
-    } else if !reference_sequences_eq(header.reference_sequences(), &reference_sequences) {
-        return Err(io::Error::new(
-            io::ErrorKind::InvalidData,
-            "SAM header and binary reference sequence dictionaries mismatch",
-        ));
+    fn raw_sam_header_reader(&mut self) -> io::Result<sam_header::Reader<R>> {
+        let len = self.inner.read_u32::<LittleEndian>().map(u64::from)?;
+        Ok(sam_header::Reader::new(self.inner, len))
     }
 
-    Ok(header)
+    fn read_reference_sequences(&mut self) -> io::Result<ReferenceSequences> {
+        read_reference_sequences(self.inner)
+    }
+}
+
+pub(super) fn read_header<R>(reader: &mut R) -> io::Result<sam::Header>
+where
+    R: Read,
+{
+    let mut header_reader = Reader::new(reader);
+    read_header_inner(&mut header_reader)
 }
 
-fn read_magic<R>(reader: &mut R) -> io::Result<()>
+fn read_magic_number<R>(reader: &mut Reader<R>) -> io::Result<()>
 where
     R: Read,
 {
-    let mut magic = [0; 4];
-    reader.read_exact(&mut magic)?;
+    let magic_number = reader.read_magic_number()?;
 
-    if magic == MAGIC_NUMBER {
+    if magic_number == MAGIC_NUMBER {
         Ok(())
     } else {
         Err(io::Error::new(
@@ -47,24 +61,44 @@ where
     }
 }
 
-fn read_header_inner<R>(reader: &mut R) -> io::Result<sam::Header>
+fn read_header_inner<R>(reader: &mut Reader<R>) -> io::Result<sam::Header>
 where
     R: Read,
 {
-    let mut parser = sam::header::Parser::default();
+    read_magic_number(reader)?;
 
-    let l_text = reader.read_u32::<LittleEndian>().map(u64::from)?;
-    let mut sam_header_reader = sam_header::Reader::new(reader, l_text);
+    let mut raw_sam_header_reader = reader.raw_sam_header_reader()?;
+    let mut header = read_sam_header(&mut raw_sam_header_reader)?;
+
+    let reference_sequences = reader.read_reference_sequences()?;
+
+    if header.reference_sequences().is_empty() {
+        *header.reference_sequences_mut() = reference_sequences;
+    } else if !reference_sequences_eq(header.reference_sequences(), &reference_sequences) {
+        return Err(io::Error::new(
+            io::ErrorKind::InvalidData,
+            "SAM header and binary reference sequence dictionaries mismatch",
+        ));
+    }
+
+    Ok(header)
+}
+
+fn read_sam_header<R>(reader: &mut sam_header::Reader<R>) -> io::Result<sam::Header>
+where
+    R: Read,
+{
+    let mut parser = sam::header::Parser::default();
 
     let mut buf = Vec::new();
 
-    while read_line(&mut sam_header_reader, &mut buf)? != 0 {
+    while read_line(reader, &mut buf)? != 0 {
         parser
             .parse_partial(&buf)
             .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
     }
 
-    sam_header_reader.discard_to_end()?;
+    reader.discard_to_end()?;
 
     Ok(parser.finish())
 }
@@ -128,22 +162,22 @@ mod tests {
     };
 
     #[test]
-    fn test_read_magic() -> io::Result<()> {
-        let data = b"BAM\x01";
-        let mut reader = &data[..];
-        assert!(read_magic(&mut reader).is_ok());
+    fn test_read_magic_number() -> io::Result<()> {
+        let mut src = &b"BAM\x01"[..];
+        let mut reader = Reader::new(&mut src);
+        assert!(read_magic_number(&mut reader).is_ok());
 
-        let data = [];
-        let mut reader = &data[..];
+        let mut src = &[][..];
+        let mut reader = Reader::new(&mut src);
         assert!(matches!(
-            read_magic(&mut reader),
+            read_magic_number(&mut reader),
             Err(ref e) if e.kind() == io::ErrorKind::UnexpectedEof
         ));
 
-        let data = b"MThd";
-        let mut reader = &data[..];
+        let mut src = &b"MThd"[..];
+        let mut reader = Reader::new(&mut src);
         assert!(matches!(
-            read_magic(&mut reader),
+            read_magic_number(&mut reader),
             Err(ref e) if e.kind() == io::ErrorKind::InvalidData
         ));
 
diff --git a/noodles-bam/src/io/reader/header/sam_header.rs b/noodles-bam/src/io/reader/header/sam_header.rs
index db551232a..ea341969b 100644
--- a/noodles-bam/src/io/reader/header/sam_header.rs
+++ b/noodles-bam/src/io/reader/header/sam_header.rs
@@ -2,16 +2,16 @@ use std::io::{self, BufRead, BufReader, Read, Take};
 
 use bstr::ByteSlice;
 
-pub(super) struct Reader<R> {
-    inner: BufReader<Take<R>>,
+pub(super) struct Reader<'r, R> {
+    inner: BufReader<Take<&'r mut R>>,
     is_eol: bool,
 }
 
-impl<R> Reader<R>
+impl<'r, R> Reader<'r, R>
 where
     R: Read,
 {
-    pub(super) fn new(inner: R, len: u64) -> Self {
+    pub(super) fn new(inner: &'r mut R, len: u64) -> Self {
         Self {
             inner: BufReader::new(inner.take(len)),
             is_eol: true,
@@ -37,7 +37,7 @@ where
     }
 }
 
-impl<R> Read for Reader<R>
+impl<R> Read for Reader<'_, R>
 where
     R: Read,
 {
@@ -49,7 +49,7 @@ where
     }
 }
 
-impl<R> BufRead for Reader<R>
+impl<R> BufRead for Reader<'_, R>
 where
     R: Read,
 {
@@ -83,10 +83,11 @@ mod tests {
     fn test_read_with_trailing_nul_padding() -> io::Result<()> {
         const DATA: &[u8] = b"@HD\tVN:1.6\n";
 
-        let mut src = DATA.to_vec();
-        src.resize(1 << 10, 0);
+        let mut buf = DATA.to_vec();
+        buf.resize(1 << 10, 0);
 
-        let mut reader = Reader::new(&src[..], 1 << 10);
+        let mut src = &buf[..];
+        let mut reader = Reader::new(&mut src, 1 << 10);
 
         let mut buf = Vec::new();
         reader.read_to_end(&mut buf)?;