diff --git a/compiler/src/test/scala/org/capnproto/TestUtil.scala b/compiler/src/test/scala/org/capnproto/TestUtil.scala
index 6dba625..dfe884e 100644
--- a/compiler/src/test/scala/org/capnproto/TestUtil.scala
+++ b/compiler/src/test/scala/org/capnproto/TestUtil.scala
@@ -35,8 +35,18 @@ object TestUtil {
       subBuilder.setFloat32Field(-1.25e-10f);
       subBuilder.setFloat64Field(345);
       subBuilder.setTextField(new Text.Reader("baz"));
+
+      {
+        val subSubBuilder = subBuilder.initStructField();
+        subSubBuilder.setTextField(new Text.Reader("nested"));
+        subSubBuilder.initStructField().setTextField(new Text.Reader("really nested"));
+      }
     }
 
+    builder.setEnumField(TestEnum.CORGE);
+
+    //builder.initVoidList(6);
+
   }
 
 
@@ -69,6 +79,11 @@ object TestUtil {
       assert(subBuilder.getUInt64Field() == 345678901234567890L);
       assert(subBuilder.getFloat32Field() == -1.25e-10f);
       assert(subBuilder.getFloat64Field() == 345);
+
+      {
+        val subSubBuilder = subBuilder.getStructField();
+        assert(subSubBuilder.getTextField().toString() == "nested")
+      }
     }
   }
 
diff --git a/runtime/src/main/java/org/capnproto/Constants.java b/runtime/src/main/java/org/capnproto/Constants.java
new file mode 100644
index 0000000..5ddbe88
--- /dev/null
+++ b/runtime/src/main/java/org/capnproto/Constants.java
@@ -0,0 +1,8 @@
+package org.capnproto;
+
+final class Constants {
+    public static final int BITS_PER_POINTER = 64;
+    public static final int BITS_PER_WORD = 64;
+    public static final int BYTES_PER_WORD = 8;
+    public static final int POINTER_SIZE_IN_WORDS = 1;
+}
diff --git a/runtime/src/main/java/org/capnproto/FieldSize.java b/runtime/src/main/java/org/capnproto/FieldSize.java
index c3043b7..e2f8604 100644
--- a/runtime/src/main/java/org/capnproto/FieldSize.java
+++ b/runtime/src/main/java/org/capnproto/FieldSize.java
@@ -9,4 +9,25 @@ public final class FieldSize {
     public static final byte EIGHT_BYTES = 5;
     public static final byte POINTER = 6;
     public static final byte INLINE_COMPOSITE = 7;
+
+    public static final int dataBitsPerElement(byte size) {
+        switch (size) {
+        case VOID: return 0;
+        case BIT: return 1;
+        case BYTE: return 8;
+        case TWO_BYTES: return 16;
+        case FOUR_BYTES: return 32;
+        case EIGHT_BYTES: return 64;
+        case POINTER: return 0;
+        case INLINE_COMPOSITE: return 0;
+        default : throw new Error("impossible field size: " + size);
+        }
+    }
+
+    public static final int pointersPerElement(byte size) {
+        switch (size) {
+        case POINTER: return 1;
+        default: return 0;
+        }
+    }
 }
diff --git a/runtime/src/main/java/org/capnproto/WireHelpers.java b/runtime/src/main/java/org/capnproto/WireHelpers.java
index 81bf98c..35498e6 100644
--- a/runtime/src/main/java/org/capnproto/WireHelpers.java
+++ b/runtime/src/main/java/org/capnproto/WireHelpers.java
@@ -6,9 +6,14 @@ final class WireHelpers {
         return (bytes + 7) / 8;
     }
 
+    public static int roundBitsUpToWords(long bits) {
+        //# This code assumes 64-bit words.
+        return (int)((bits + 63) / ((long) Constants.BITS_PER_WORD));
+    }
+
     public static int allocate(int refOffset,
                                SegmentBuilder segment,
-                               int amount,
+                               int amount, // in words
                                byte kind) {
 
         // TODO check for nullness, amount == 0 case.
@@ -65,7 +70,20 @@ final class WireHelpers {
                                               SegmentBuilder segment,
                                               int elementCount,
                                               byte elementSize) {
-        throw new Error("unimplemented");
+        if (elementSize == FieldSize.INLINE_COMPOSITE) {
+            throw new DecodeException("Should have called initStructListPointer instead");
+        }
+
+        int dataSize = FieldSize.dataBitsPerElement(elementSize);
+        int pointerCount = FieldSize.pointersPerElement(elementSize);
+        int step = dataSize + pointerCount * Constants.BITS_PER_POINTER;
+        int wordCount = roundBitsUpToWords((long)elementCount * (long)step);
+        int ptr = allocate(refOffset, segment, wordCount, WirePointer.LIST);
+
+        ListPointer.set(segment.buffer, refOffset, elementSize, elementCount);
+
+        return new ListBuilder(segment, ptr * Constants.BYTES_PER_WORD,
+                               elementCount, step, dataSize, (short)pointerCount);
     }
 
     public static ListBuilder initStructListPointer(int refOffset,
@@ -82,7 +100,8 @@ final class WireHelpers {
 
         //# Allocate the list, prefixed by a single WirePointer.
         int wordCount = elementCount * wordsPerElement;
-        int ptrOffset = allocate(refOffset, segment, 1 + wordCount, WirePointer.LIST);
+        int ptrOffset = allocate(refOffset, segment, Constants.POINTER_SIZE_IN_WORDS + wordCount,
+                                 WirePointer.LIST);
 
         //# Initialize the pointer.
         ListPointer.setInlineComposite(segment.buffer, refOffset, wordCount);