diff --git a/src/codec/length_delimited.rs b/src/codec/length_delimited.rs
index 54ec202bb..b47886513 100644
--- a/src/codec/length_delimited.rs
+++ b/src/codec/length_delimited.rs
@@ -578,6 +578,10 @@ impl Encoder for LengthDelimitedCodec {
             "provided length would overflow after adjustment",
         ))?;
 
+        // Reserve capacity in the destination buffer to fit the frame and
+        // length field (plus adjustment).
+        dst.reserve(self.builder.length_field_len + n);
+
         if self.builder.length_field_is_big_endian {
             dst.put_uint_be(n as u64, self.builder.length_field_len);
         } else {
diff --git a/tests/length_delimited.rs b/tests/length_delimited.rs
index 318f35ef3..4e118d379 100644
--- a/tests/length_delimited.rs
+++ b/tests/length_delimited.rs
@@ -5,7 +5,7 @@ extern crate bytes;
 use tokio::io::{AsyncRead, AsyncWrite};
 use tokio::codec::*;
 
-use bytes::Bytes;
+use bytes::{Bytes, BytesMut, BufMut};
 use futures::{Stream, Sink, Poll};
 use futures::Async::*;
 
@@ -483,6 +483,22 @@ fn write_zero() {
     assert!(io.get_ref().calls.is_empty());
 }
 
+#[test]
+fn encode_overflow() {
+    // Test reproducing tokio-rs/tokio#681.
+    let mut codec = length_delimited::Builder::new().new_codec();
+    let mut buf = BytesMut::with_capacity(1024);
+
+    // Put some data into the buffer without resizing it to hold more.
+    let some_as = std::iter::repeat(b'a')
+        .take(1024)
+        .collect::<Vec<_>>();
+    buf.put_slice(&some_as[..]);
+
+    // Trying to encode the length header should resize the buffer if it won't fit.
+    codec.encode(Bytes::from("hello"), &mut buf).unwrap();
+}
+
 // ===== Test utils =====
 
 fn would_block() -> io::Error {