diff --git a/runtime/src/main/java/org/capnproto/BuilderArena.java b/runtime/src/main/java/org/capnproto/BuilderArena.java
index ccfeb23..bcd5cf5 100644
--- a/runtime/src/main/java/org/capnproto/BuilderArena.java
+++ b/runtime/src/main/java/org/capnproto/BuilderArena.java
@@ -13,6 +13,7 @@ public final class BuilderArena implements Arena {
         this.segments = new Vector<SegmentBuilder>();
         SegmentBuilder segment0 = new SegmentBuilder(ByteBuffer.allocate(1024 * 8));
         segment0.buffer.mark();
+        segment0.buffer.order(ByteOrder.LITTLE_ENDIAN);
         this.segments.add(segment0);
     }