diff --git a/src/archive.rs b/src/archive.rs
index a3830ff..491f1eb 100644
--- a/src/archive.rs
+++ b/src/archive.rs
@@ -15,6 +15,7 @@ use tokio::{
 };
 use tokio_stream::*;
 
+use crate::header::BLOCK_SIZE;
 use crate::{
     entry::{EntryFields, EntryIo},
     error::TarError,
@@ -435,7 +436,7 @@ fn poll_next_raw<R: Read + Unpin>(
         // Otherwise, check if we are ignoring zeros and continue, or break as if this is the
         // end of the archive.
         if !header.as_bytes().iter().all(|i| *i == 0) {
-            *next += 512;
+            *next += BLOCK_SIZE;
             break;
         }
 
@@ -443,7 +444,7 @@ fn poll_next_raw<R: Read + Unpin>(
             return Poll::Ready(None);
         }
 
-        *next += 512;
+        *next += BLOCK_SIZE;
         header_pos = *next;
     }
 
@@ -486,10 +487,10 @@ fn poll_next_raw<R: Read + Unpin>(
     // Store where the next entry is, rounding up by 512 bytes (the size of
     // a header);
     let size = size
-        .checked_add(511)
+        .checked_add(BLOCK_SIZE - 1)
         .ok_or_else(|| other("size overflow"))?;
     *next = next
-        .checked_add(size & !511)
+        .checked_add(size & !(BLOCK_SIZE - 1))
         .ok_or_else(|| other("size overflow"))?;
 
     Poll::Ready(Some(Ok(ret.into_entry())))
@@ -546,7 +547,7 @@ fn poll_parse_sparse_header<R: Read + Unpin>(
             let off = block.offset()?;
             let len = block.length()?;
 
-            if len != 0 && (size - remaining) % 512 != 0 {
+            if len != 0 && (size - remaining) % BLOCK_SIZE != 0 {
                 return Err(other(
                     "previous block in sparse file was not \
                      aligned to 512-byte boundary",
@@ -597,7 +598,7 @@ fn poll_parse_sparse_header<R: Read + Unpin>(
                     Err(err) => return Poll::Ready(Err(err)),
                 }
 
-                *next += 512;
+                *next += BLOCK_SIZE;
                 for block in ext.sparse.iter() {
                     add_block(block)?;
                 }
diff --git a/src/header.rs b/src/header.rs
index 545bb73..a506d2b 100644
--- a/src/header.rs
+++ b/src/header.rs
@@ -25,11 +25,13 @@ use crate::{other, EntryType};
 #[cfg(any(unix, windows))]
 const DETERMINISTIC_TIMESTAMP: u64 = 1153704088;
 
+pub(crate) const BLOCK_SIZE: u64 = 512;
+
 /// Representation of the header of an entry in an archive
 #[repr(C)]
 #[allow(missing_docs)]
 pub struct Header {
-    bytes: [u8; 512],
+    bytes: [u8; BLOCK_SIZE as usize],
 }
 
 /// Declares the information that should be included when filling a Header
@@ -148,7 +150,9 @@ impl Header {
     /// extensions such as long path names, long link names, and setting the
     /// atime/ctime metadata attributes of files.
     pub fn new_gnu() -> Header {
-        let mut header = Header { bytes: [0; 512] };
+        let mut header = Header {
+            bytes: [0; BLOCK_SIZE as usize],
+        };
         unsafe {
             let gnu = cast_mut::<_, GnuHeader>(&mut header);
             gnu.magic = *b"ustar ";
@@ -166,7 +170,9 @@ impl Header {
     ///
     /// UStar is also the basis used for pax archives.
     pub fn new_ustar() -> Header {
-        let mut header = Header { bytes: [0; 512] };
+        let mut header = Header {
+            bytes: [0; BLOCK_SIZE as usize],
+        };
         unsafe {
             let gnu = cast_mut::<_, UstarHeader>(&mut header);
             gnu.magic = *b"ustar\0";
@@ -183,7 +189,9 @@ impl Header {
     /// format limits the path name limit and isn't able to contain extra
     /// metadata like atime/ctime.
     pub fn new_old() -> Header {
-        let mut header = Header { bytes: [0; 512] };
+        let mut header = Header {
+            bytes: [0; BLOCK_SIZE as usize],
+        };
         header.set_mtime(0);
         header
     }
@@ -273,12 +281,12 @@ impl Header {
     }
 
     /// Returns a view into this header as a byte array.
-    pub fn as_bytes(&self) -> &[u8; 512] {
+    pub fn as_bytes(&self) -> &[u8; BLOCK_SIZE as usize] {
         &self.bytes
     }
 
     /// Returns a view into this header as a byte array.
-    pub fn as_mut_bytes(&mut self) -> &mut [u8; 512] {
+    pub fn as_mut_bytes(&mut self) -> &mut [u8; BLOCK_SIZE as usize] {
         &mut self.bytes
     }
 
@@ -1367,15 +1375,15 @@ impl GnuExtSparseHeader {
     }
 
     /// Returns a view into this header as a byte array.
-    pub fn as_bytes(&self) -> &[u8; 512] {
-        debug_assert_eq!(mem::size_of_val(self), 512);
-        unsafe { &*(self as *const GnuExtSparseHeader as *const [u8; 512]) }
+    pub fn as_bytes(&self) -> &[u8; BLOCK_SIZE as usize] {
+        debug_assert_eq!(mem::size_of_val(self), BLOCK_SIZE as usize);
+        unsafe { &*(self as *const GnuExtSparseHeader as *const [u8; BLOCK_SIZE as usize]) }
     }
 
     /// Returns a view into this header as a byte array.
-    pub fn as_mut_bytes(&mut self) -> &mut [u8; 512] {
-        debug_assert_eq!(mem::size_of_val(self), 512);
-        unsafe { &mut *(self as *mut GnuExtSparseHeader as *mut [u8; 512]) }
+    pub fn as_mut_bytes(&mut self) -> &mut [u8; BLOCK_SIZE as usize] {
+        debug_assert_eq!(mem::size_of_val(self), BLOCK_SIZE as usize);
+        unsafe { &mut *(self as *mut GnuExtSparseHeader as *mut [u8; BLOCK_SIZE as usize]) }
     }
 
     /// Returns a slice of the underlying sparse headers.