diff --git a/runtime/src/main/java/org/capnproto/CallContext.java b/runtime/src/main/java/org/capnproto/CallContext.java
index 9429250..55b58cd 100644
--- a/runtime/src/main/java/org/capnproto/CallContext.java
+++ b/runtime/src/main/java/org/capnproto/CallContext.java
@@ -32,7 +32,7 @@ public class CallContext<Params, Results> {
         return this.hook.getResults().initAs(results);
     }
 
-    public final <SubParams, Results> CompletableFuture<?> tailCall(Request<SubParams, Results> tailRequest) {
+    public final <SubParams, Results> CompletableFuture<java.lang.Void> tailCall(Request<SubParams, Results> tailRequest) {
         return this.hook.tailCall(tailRequest.getHook());
     }
 
diff --git a/runtime/src/main/java/org/capnproto/CallContextHook.java b/runtime/src/main/java/org/capnproto/CallContextHook.java
index 08f85c9..461db7c 100644
--- a/runtime/src/main/java/org/capnproto/CallContextHook.java
+++ b/runtime/src/main/java/org/capnproto/CallContextHook.java
@@ -13,7 +13,7 @@ public interface CallContextHook {
 
     AnyPointer.Builder getResults(int sizeHint);
 
-    CompletableFuture<?> tailCall(RequestHook request);
+    CompletableFuture<java.lang.Void> tailCall(RequestHook request);
 
     void allowCancellation();
 
diff --git a/runtime/src/main/java/org/capnproto/PipelineHook.java b/runtime/src/main/java/org/capnproto/PipelineHook.java
index 8d12f22..50c1ac3 100644
--- a/runtime/src/main/java/org/capnproto/PipelineHook.java
+++ b/runtime/src/main/java/org/capnproto/PipelineHook.java
@@ -1,10 +1,14 @@
 package org.capnproto;
 
 public interface PipelineHook {
-
     ClientHook getPipelinedCap(PipelineOp[] ops);
 
     static PipelineHook newBrokenPipeline(Throwable exc) {
-        return ops -> Capability.newBrokenCap(exc);
+        return new PipelineHook() {
+            @Override
+            public ClientHook getPipelinedCap(PipelineOp[] ops) {
+                return Capability.newBrokenCap(exc);
+            }
+        };
     }
 }