diff --git a/src/lib.rs b/src/lib.rs
index 7f03f81..40e952b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -9,12 +9,12 @@
 use std::{io, mem, ptr, slice};
 
 #[inline]
-pub fn write<W: io::Write, V: Integer>(wr: W, value: V) -> io::Result<()> {
+pub fn write<W: io::Write, V: Integer>(wr: W, value: V) -> io::Result<usize> {
     value.write(wr)
 }
 
 pub trait Integer {
-    fn write<W: io::Write>(self, W) -> io::Result<()>;
+    fn write<W: io::Write>(self, W) -> io::Result<usize>;
 }
 
 const DEC_DIGITS_LUT: &'static[u8] =
@@ -30,7 +30,7 @@ macro_rules! impl_Integer {
     ($($t:ident),* as $conv_fn:ident) => ($(
     impl Integer for $t {
         #[allow(unused_comparisons)]
-        fn write<W: io::Write>(self, mut wr: W) -> io::Result<()> {
+        fn write<W: io::Write>(self, mut wr: W) -> io::Result<usize> {
             let is_nonnegative = self >= 0;
             let mut n = if is_nonnegative {
                 self as $conv_fn
@@ -81,9 +81,12 @@ macro_rules! impl_Integer {
                 }
             }
 
-            wr.write_all(unsafe {
-                slice::from_raw_parts(buf_ptr.offset(curr), buf.len() - curr as usize)
-            })
+            let mut len = buf.len() - curr as usize;
+            try!(wr.write_all(unsafe { slice::from_raw_parts(buf_ptr.offset(curr), len) }));
+            if !is_nonnegative {
+                len += 1;
+            }
+            Ok(len)
         }
     })*);
 }
diff --git a/tests/test.rs b/tests/test.rs
index 83ad59a..7615c19 100644
--- a/tests/test.rs
+++ b/tests/test.rs
@@ -7,9 +7,9 @@ macro_rules! test {
         $(
             #[test]
             fn $name() {
-                let mut buf = Vec::with_capacity(20);
-                itoa::write(&mut buf, $value).unwrap();
-                assert_eq!(buf, $expected.as_bytes());
+                let mut buf = [b'\0'; 20];
+                let len = itoa::write(&mut buf[..], $value).unwrap();
+                assert_eq!(&buf[0..len], $expected.as_bytes());
             }
         )*
     }