diff --git a/runtime/src/main/java/org/capnproto/Allocator.java b/runtime/src/main/java/org/capnproto/Allocator.java
index 71093ad..a67bb7f 100644
--- a/runtime/src/main/java/org/capnproto/Allocator.java
+++ b/runtime/src/main/java/org/capnproto/Allocator.java
@@ -3,7 +3,7 @@ package org.capnproto;
 /**
  * An object that allocates memory for a Cap'n Proto message as it is being built.
  */
-interface Allocator {
+public interface Allocator {
     /**
      * Allocates a ByteBuffer to be used as a segment in a message. The returned
      * buffer must contain at least `minimumSize` bytes, all of which MUST be