diff --git a/src/libstd/io/mod.rs b/src/libstd/io/mod.rs
index 37c3f70d54dda..193f396c0d4ab 100644
--- a/src/libstd/io/mod.rs
+++ b/src/libstd/io/mod.rs
@@ -289,7 +289,7 @@ mod lazy;
 mod util;
 mod stdio;
 
-const DEFAULT_BUF_SIZE: usize = 8 * 1024;
+const DEFAULT_BUF_SIZE: usize = ::sys_common::io::DEFAULT_BUF_SIZE;
 
 // A few methods below (read_to_string, read_line) will append data into a
 // `String` buffer, but we need to be pretty careful when doing this. The
diff --git a/src/libstd/io/stdio.rs b/src/libstd/io/stdio.rs
index c24ee8ff303c8..1777b79ea1b59 100644
--- a/src/libstd/io/stdio.rs
+++ b/src/libstd/io/stdio.rs
@@ -214,15 +214,7 @@ pub fn stdin() -> Stdin {
             _ => Maybe::Fake
         };
 
-        // The default buffer capacity is 64k, but apparently windows
-        // doesn't like 64k reads on stdin. See #13304 for details, but the
-        // idea is that on windows we use a slightly smaller buffer that's
-        // been seen to be acceptable.
-        Arc::new(Mutex::new(if cfg!(windows) {
-            BufReader::with_capacity(8 * 1024, stdin)
-        } else {
-            BufReader::new(stdin)
-        }))
+        Arc::new(Mutex::new(BufReader::with_capacity(stdio::STDIN_BUF_SIZE, stdin)))
     }
 }
 
diff --git a/src/libstd/sys/common/io.rs b/src/libstd/sys/common/io.rs
index 0483725dd83bc..23daeeb5187b7 100644
--- a/src/libstd/sys/common/io.rs
+++ b/src/libstd/sys/common/io.rs
@@ -12,6 +12,8 @@ use io::ErrorKind;
 use io::Read;
 use slice::from_raw_parts_mut;
 
+pub const DEFAULT_BUF_SIZE: usize = 8 * 1024;
+
 // Provides read_to_end functionality over an uninitialized buffer.
 // This function is unsafe because it calls the underlying
 // read function with a slice into uninitialized memory. The default
diff --git a/src/libstd/sys/unix/stdio.rs b/src/libstd/sys/unix/stdio.rs
index 947ba2cc75232..273341b1918d1 100644
--- a/src/libstd/sys/unix/stdio.rs
+++ b/src/libstd/sys/unix/stdio.rs
@@ -67,3 +67,4 @@ impl io::Write for Stderr {
 }
 
 pub const EBADF_ERR: i32 = ::libc::EBADF as i32;
+pub const STDIN_BUF_SIZE: usize = ::sys_common::io::DEFAULT_BUF_SIZE;
diff --git a/src/libstd/sys/windows/stdio.rs b/src/libstd/sys/windows/stdio.rs
index 5f097d2631d95..72788776dedd6 100644
--- a/src/libstd/sys/windows/stdio.rs
+++ b/src/libstd/sys/windows/stdio.rs
@@ -207,3 +207,8 @@ fn invalid_encoding() -> io::Error {
 }
 
 pub const EBADF_ERR: i32 = ::sys::c::ERROR_INVALID_HANDLE as i32;
+// The default buffer capacity is 64k, but apparently windows
+// doesn't like 64k reads on stdin. See #13304 for details, but the
+// idea is that on windows we use a slightly smaller buffer that's
+// been seen to be acceptable.
+pub const STDIN_BUF_SIZE: usize = 8 * 1024;
diff --git a/src/tools/tidy/src/pal.rs b/src/tools/tidy/src/pal.rs
index 80a2d22691b8b..6ce5f7ee7fe27 100644
--- a/src/tools/tidy/src/pal.rs
+++ b/src/tools/tidy/src/pal.rs
@@ -66,7 +66,6 @@ const EXCEPTION_PATHS: &'static [&'static str] = &[
     "src/libstd/lib.rs", // This could probably be done within the sys directory
     "src/libstd/rtdeps.rs", // Until rustbuild replaces make
     "src/libstd/path.rs",
-    "src/libstd/io/stdio.rs",
     "src/libstd/num/f32.rs",
     "src/libstd/num/f64.rs",
     "src/libstd/sys/common/mod.rs",