diff --git a/src/message.js b/src/message.js
index 7d6224f..1596985 100644
--- a/src/message.js
+++ b/src/message.js
@@ -149,11 +149,13 @@ function multipartEncode(
     const contentArray = new Uint8Array(datasetBuffer);
     const contentLength = contentArray.length;
 
-    length += headerLength + contentLength + footerLength;
+    length += headerLength + contentLength;
 
     return contentArray;
   });
 
+  length += footerLength;
+
   // Allocate the array
   const multipartArray = new Uint8Array(length);