diff --git a/dart/lib/flat_buffers.dart b/dart/lib/flat_buffers.dart
index 0f4ccbccf..99fd6a2d5 100644
--- a/dart/lib/flat_buffers.dart
+++ b/dart/lib/flat_buffers.dart
@@ -670,6 +670,7 @@ class Builder {
     for (int i = 0; i < length; i++) {
       _buf.setUint8(offset++, bytes[i]);
     }
+    _buf.setUint8(offset, 0); // trailing zero
     return result;
   }