diff --git a/core/pom.xml b/core/pom.xml
index a6abf30d56..9f1b049474 100644
--- a/core/pom.xml
+++ b/core/pom.xml
@@ -99,7 +99,7 @@
         <dependency>
             <groupId>com.google.guava</groupId>
             <artifactId>guava</artifactId>
-            <version>11.0.2</version>
+            <version>12.0-rc1</version>
         </dependency>
     </dependencies>
 
diff --git a/labs/virtualbox/src/main/java/org/jclouds/virtualbox/functions/MastersLoadingCache.java b/labs/virtualbox/src/main/java/org/jclouds/virtualbox/functions/MastersLoadingCache.java
index ecdc4b8bc3..5aa668205e 100644
--- a/labs/virtualbox/src/main/java/org/jclouds/virtualbox/functions/MastersLoadingCache.java
+++ b/labs/virtualbox/src/main/java/org/jclouds/virtualbox/functions/MastersLoadingCache.java
@@ -19,12 +19,14 @@
 
 package org.jclouds.virtualbox.functions;
 
+import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.base.Preconditions.checkState;
-import static org.jclouds.virtualbox.config.VirtualBoxConstants.*;
+import static org.jclouds.virtualbox.config.VirtualBoxConstants.VIRTUALBOX_DEFAULT_DIR;
 import static org.jclouds.virtualbox.config.VirtualBoxConstants.VIRTUALBOX_IMAGE_PREFIX;
 import static org.jclouds.virtualbox.config.VirtualBoxConstants.VIRTUALBOX_INSTALLATION_KEY_SEQUENCE;
 import static org.jclouds.virtualbox.config.VirtualBoxConstants.VIRTUALBOX_NODE_NAME_SEPARATOR;
+import static org.jclouds.virtualbox.config.VirtualBoxConstants.VIRTUALBOX_PRECONFIGURATION_URL;
 import static org.jclouds.virtualbox.config.VirtualBoxConstants.VIRTUALBOX_WORKINGDIR;
 import static org.jclouds.virtualbox.util.MachineUtils.machineNotFoundException;
 
@@ -215,9 +217,11 @@ public class MastersLoadingCache extends AbstractLoadingCache<Image, Master> {
    }
 
    @Override
-   public synchronized Master getIfPresent(Image key) {
-      if (masters.containsKey(key.getId())) {
-         return masters.get(key.getId());
+   public synchronized Master getIfPresent(Object key) {
+      checkArgument(key instanceof Image, "this cache is for entries who's keys are Images");
+      Image image = Image.class.cast(key);
+      if (masters.containsKey(image.getId())) {
+         return masters.get(image.getId());
       }
       return null;
    }