diff --git a/runtime/src/main/java/org/capnproto/DefaultAllocator.java b/runtime/src/main/java/org/capnproto/DefaultAllocator.java
index 72cd344..d136356 100644
--- a/runtime/src/main/java/org/capnproto/DefaultAllocator.java
+++ b/runtime/src/main/java/org/capnproto/DefaultAllocator.java
@@ -4,7 +4,7 @@ import java.nio.ByteBuffer;
 
 import org.capnproto.BuilderArena.AllocationStrategy;
 
-class DefaultAllocator implements Allocator {
+public class DefaultAllocator implements Allocator {
 
     // (minimum) number of bytes in the next allocation
     private int nextSize = BuilderArena.SUGGESTED_FIRST_SEGMENT_WORDS;
@@ -18,6 +18,8 @@ class DefaultAllocator implements Allocator {
     public AllocationStrategy allocationStrategy =
         AllocationStrategy.GROW_HEURISTICALLY;
 
+    public DefaultAllocator() {}
+
     public DefaultAllocator(AllocationStrategy allocationStrategy) {
         this.allocationStrategy = allocationStrategy;
     }