diff --git a/Cargo.lock b/Cargo.lock
index 58162ba6..c1128994 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3563,7 +3563,7 @@ version = "0.8.3"
 dependencies = [
  "async-io 1.13.0",
  "async-std",
- "base64 0.22.0",
+ "base64 0.22.1",
  "bigdecimal",
  "bit-vec",
  "bstr",
diff --git a/sqlx-postgres/src/copy.rs b/sqlx-postgres/src/copy.rs
index ddc187e9..fd9ed7e8 100644
--- a/sqlx-postgres/src/copy.rs
+++ b/sqlx-postgres/src/copy.rs
@@ -230,10 +230,10 @@ impl<C: DerefMut<Target = PgConnection>> PgCopyIn<C> {
             }
 
             // Write the length
-            let read32 = u32::try_from(read)
-                .map_err(|_| err_protocol!("number of bytes read exceeds 2^32: {}", read))?;
+            let read32 = i32::try_from(read)
+                .map_err(|_| err_protocol!("number of bytes read exceeds 2^31 - 1: {}", read))?;
 
-            (&mut buf.get_mut()[1..]).put_u32(read32 + 4);
+            (&mut buf.get_mut()[1..]).put_i32(read32 + 4);
 
             conn.inner.stream.flush().await?;
         }