diff --git a/tokio-util/src/codec/length_delimited.rs b/tokio-util/src/codec/length_delimited.rs
index 8a7efbbdc..abc6461b5 100644
--- a/tokio-util/src/codec/length_delimited.rs
+++ b/tokio-util/src/codec/length_delimited.rs
@@ -631,8 +631,8 @@ impl Encoder<Bytes> for LengthDelimitedCodec {
         })?;
 
         // Reserve capacity in the destination buffer to fit the frame and
-        // length field (plus adjustment).
-        dst.reserve(self.builder.length_field_len + n);
+        // length field.
+        dst.reserve(self.builder.length_field_len + data.len());
 
         if self.builder.length_field_is_big_endian {
             dst.put_uint(n as u64, self.builder.length_field_len);