diff --git a/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/config/NovaRestClientModule.java b/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/config/NovaRestClientModule.java
index 3db26f9ca6..579b62390f 100644
--- a/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/config/NovaRestClientModule.java
+++ b/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/config/NovaRestClientModule.java
@@ -78,6 +78,7 @@ import com.google.common.cache.CacheBuilder;
 import com.google.common.cache.CacheLoader;
 import com.google.common.cache.LoadingCache;
 import com.google.common.collect.ImmutableMap;
+import com.google.common.reflect.TypeToken;
 import com.google.inject.Provides;
 
 /**
@@ -86,11 +87,13 @@ import com.google.inject.Provides;
  * @author Adrian Cole
  */
 @ConfiguresRestClient
-public class NovaRestClientModule extends RestClientModule<NovaApi, NovaAsyncApi> {
+public class NovaRestClientModule<S extends NovaApi, A extends NovaAsyncApi> extends RestClientModule<S, A> {
 
    public static final Map<Class<?>, Class<?>> DELEGATE_MAP = ImmutableMap.<Class<?>, Class<?>> builder()
-         .put(ServerApi.class, ServerAsyncApi.class).put(FlavorApi.class, FlavorAsyncApi.class)
-         .put(ImageApi.class, ImageAsyncApi.class).put(ExtensionApi.class, ExtensionAsyncApi.class)
+         .put(ServerApi.class, ServerAsyncApi.class)
+         .put(FlavorApi.class, FlavorAsyncApi.class)
+         .put(ImageApi.class, ImageAsyncApi.class)
+         .put(ExtensionApi.class, ExtensionAsyncApi.class)
          .put(FloatingIPApi.class, FloatingIPAsyncApi.class)
          .put(SecurityGroupApi.class, SecurityGroupAsyncApi.class)
          .put(KeyPairApi.class, KeyPairAsyncApi.class)
@@ -106,9 +109,14 @@ public class NovaRestClientModule extends RestClientModule<NovaApi, NovaAsyncApi
          .put(QuotaClassApi.class, QuotaClassAsyncApi.class)
          .put(VolumeTypeApi.class, VolumeTypeAsyncApi.class)
          .build();
-
+   
    public NovaRestClientModule() {
-      super(DELEGATE_MAP);
+      super(TypeToken.class.cast(TypeToken.of(NovaApi.class)), TypeToken.class.cast(TypeToken.of(NovaAsyncApi.class)), DELEGATE_MAP);
+   }
+
+   protected NovaRestClientModule(TypeToken<S> syncClientType, TypeToken<A> asyncClientType,
+            Map<Class<?>, Class<?>> sync2Async) {
+      super(syncClientType, asyncClientType, sync2Async);
    }
 
    @Override
diff --git a/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/features/ServerApi.java b/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/features/ServerApi.java
index 7d73f50349..8b476a669e 100644
--- a/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/features/ServerApi.java
+++ b/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/features/ServerApi.java
@@ -54,7 +54,7 @@ public interface ServerApi {
     * 
     * @return all servers (all details)
     */
-   Set<Server> listServersInDetail();
+   Set<? extends Server> listServersInDetail();
 
    /**
     * List details of the specified server
diff --git a/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/features/ServerAsyncApi.java b/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/features/ServerAsyncApi.java
index 00355d83df..538f35f263 100644
--- a/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/features/ServerAsyncApi.java
+++ b/apis/openstack-nova/src/main/java/org/jclouds/openstack/nova/v2_0/features/ServerAsyncApi.java
@@ -86,7 +86,7 @@ public interface ServerAsyncApi {
    @Consumes(MediaType.APPLICATION_JSON)
    @Path("/servers/detail")
    @ExceptionParser(ReturnEmptySetOnNotFoundOr404.class)
-   ListenableFuture<Set<Server>> listServersInDetail();
+   ListenableFuture<? extends Set<? extends Server>> listServersInDetail();
 
    /**
     * @see ServerApi#getServer
@@ -96,7 +96,7 @@ public interface ServerAsyncApi {
    @Consumes(MediaType.APPLICATION_JSON)
    @Path("/servers/{id}")
    @ExceptionParser(ReturnNullOnNotFoundOr404.class)
-   ListenableFuture<Server> getServer(@PathParam("id") String id);
+   ListenableFuture<? extends Server> getServer(@PathParam("id") String id);
 
    /**
     * @see ServerApi#deleteServer