diff --git a/benchmark/src/main/java/org/capnproto/benchmark/TestCase.java b/benchmark/src/main/java/org/capnproto/benchmark/TestCase.java
index 13a45e6..c1b7980 100644
--- a/benchmark/src/main/java/org/capnproto/benchmark/TestCase.java
+++ b/benchmark/src/main/java/org/capnproto/benchmark/TestCase.java
@@ -1,5 +1,6 @@
 package org.capnproto.benchmark;
 
+import java.io.IOException;
 import java.nio.ByteBuffer;
 
 import org.capnproto.FromStructReader;
@@ -37,7 +38,7 @@ public abstract class TestCase<RequestFactory extends StructFactory<RequestBuild
     static final int SCRATCH_SIZE = 128 * 1024;
 
     public void passByBytes(RequestFactory requestFactory, ResponseFactory responseFactory,
-                            long iters) {
+                            long iters) throws IOException {
 
         ByteBuffer requestBytes = ByteBuffer.allocate(SCRATCH_SIZE * 8);
         ByteBuffer responseBytes = ByteBuffer.allocate(SCRATCH_SIZE * 8);
@@ -52,8 +53,9 @@ public abstract class TestCase<RequestFactory extends StructFactory<RequestBuild
 
             {
                 org.capnproto.ByteBufferWritableByteChannel writer = new org.capnproto.ByteBufferWritableByteChannel(requestBytes);
-                //org.capnproto.writeMessage
+                org.capnproto.Serialize.writeMessage(writer, requestMessage);
             }
+
             // TODO
             throw new Error("unimplemented");
         }
@@ -72,12 +74,16 @@ public abstract class TestCase<RequestFactory extends StructFactory<RequestBuild
         String compression = args[2];
         long iters = Long.parseLong(args[3]);
 
-        if (mode.equals("object")) {
-            passByObject(requestFactory, responseFactory, iters);
-        } else if (mode.equals("bytes")) {
-            passByBytes(requestFactory, responseFactory, iters);
-        } else {
-            System.out.println("unknown mode: " + mode);
+        try {
+            if (mode.equals("object")) {
+                passByObject(requestFactory, responseFactory, iters);
+            } else if (mode.equals("bytes")) {
+                passByBytes(requestFactory, responseFactory, iters);
+            } else {
+                System.out.println("unknown mode: " + mode);
+            }
+        } catch (IOException e) {
+            System.err.println("IOException: " + e);
         }
     }
 }
diff --git a/runtime/src/main/java/org/capnproto/Serialize.java b/runtime/src/main/java/org/capnproto/Serialize.java
index 2053cc1..0188914 100644
--- a/runtime/src/main/java/org/capnproto/Serialize.java
+++ b/runtime/src/main/java/org/capnproto/Serialize.java
@@ -1,20 +1,13 @@
 package org.capnproto;
 
 import java.io.IOException;
-import java.nio.channels.GatheringByteChannel;
+import java.nio.channels.WritableByteChannel;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 
 public final class Serialize {
 
-    static boolean hasRemaining(ByteBuffer[] buffers) {
-        for (ByteBuffer buffer : buffers) {
-            if (buffer.hasRemaining()) { return true; }
-        }
-        return false;
-    }
-
-    public static void writeMessage(GatheringByteChannel outputChannel,
+    public static void writeMessage(WritableByteChannel outputChannel,
                                     MessageBuilder message) throws IOException {
         ByteBuffer[] segments = message.getSegmentsForOutput();
         int tableSize = (segments.length + 2) & (~1);
@@ -33,9 +26,10 @@ public final class Serialize {
             outputChannel.write(table);
         }
 
-        while (hasRemaining(segments)) {
-            outputChannel.write(segments);
-            // TODO check for results of 0 or -1.
+        for (ByteBuffer buffer : segments) {
+            while(buffer.hasRemaining()) {
+                outputChannel.write(buffer);
+            }
         }
     }
 }