diff --git a/language-adaptors/rxjava-clojure/src/main/java/org/rx/lang/clojure/ClojureAdaptor.java b/language-adaptors/rxjava-clojure/src/main/java/org/rx/lang/clojure/ClojureAdaptor.java
index 65414b982f..70c9084dc3 100644
--- a/language-adaptors/rxjava-clojure/src/main/java/org/rx/lang/clojure/ClojureAdaptor.java
+++ b/language-adaptors/rxjava-clojure/src/main/java/org/rx/lang/clojure/ClojureAdaptor.java
@@ -15,8 +15,6 @@
  */
 package org.rx.lang.clojure;
 
-import static org.mockito.Mockito.*;
-
 import java.util.Arrays;
 
 import org.junit.Before;
@@ -82,8 +80,8 @@ public Object call(Object function, Object[] args) {
     }
 
     @Override
-    public Class<?> getFunctionClass() {
-        return IFn.class;
+    public Class<?>[] getFunctionClass() {
+        return new Class<?>[] { IFn.class };
     }
 
     public static class UnitTest {
diff --git a/language-adaptors/rxjava-groovy/src/main/java/org/rx/lang/groovy/GroovyAdaptor.java b/language-adaptors/rxjava-groovy/src/main/java/org/rx/lang/groovy/GroovyAdaptor.java
index d8a0b5f871..bdff61a06a 100644
--- a/language-adaptors/rxjava-groovy/src/main/java/org/rx/lang/groovy/GroovyAdaptor.java
+++ b/language-adaptors/rxjava-groovy/src/main/java/org/rx/lang/groovy/GroovyAdaptor.java
@@ -1,12 +1,12 @@
 /**
  * Copyright 2013 Netflix, Inc.
- *
+ * 
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -41,8 +41,8 @@ public Object call(Object function, Object[] args) {
         return ((Closure<?>) function).call(args);
     }
 
-    public Class<?> getFunctionClass() {
-        return Closure.class;
+    public Class<?>[] getFunctionClass() {
+        return new Class<?>[] { Closure.class };
     }
 
     public static class UnitTest {
diff --git a/language-adaptors/rxjava-jruby/src/main/java/org/rx/lang/jruby/JRubyAdaptor.java b/language-adaptors/rxjava-jruby/src/main/java/org/rx/lang/jruby/JRubyAdaptor.java
index 8a9d53e699..e101c809fb 100644
--- a/language-adaptors/rxjava-jruby/src/main/java/org/rx/lang/jruby/JRubyAdaptor.java
+++ b/language-adaptors/rxjava-jruby/src/main/java/org/rx/lang/jruby/JRubyAdaptor.java
@@ -1,12 +1,12 @@
 /**
  * Copyright 2013 Netflix, Inc.
- *
+ * 
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -49,8 +49,8 @@ public Object call(Object function, Object[] args) {
     }
 
     @Override
-    public Class<?> getFunctionClass() {
-        return RubyProc.class;
+    public Class<?>[] getFunctionClass() {
+        return new Class<?>[] { RubyProc.class };
     }
 
     public static class UnitTest {
diff --git a/rxjava-core/src/main/java/org/rx/functions/FunctionLanguageAdaptor.java b/rxjava-core/src/main/java/org/rx/functions/FunctionLanguageAdaptor.java
index 8ec16b390e..dfbd735b24 100644
--- a/rxjava-core/src/main/java/org/rx/functions/FunctionLanguageAdaptor.java
+++ b/rxjava-core/src/main/java/org/rx/functions/FunctionLanguageAdaptor.java
@@ -30,8 +30,10 @@ public interface FunctionLanguageAdaptor {
      * The Class of the Function that this adaptor serves.
      * <p>
      * Example: groovy.lang.Closure
+     * <p>
+     * This should not return classes of java.* packages.
      * 
-     * @return Class
+     * @return Class[] of classes that this adaptor should be invoked for.
      */
-    public Class<?> getFunctionClass();
+    public Class<?>[] getFunctionClass();
 }
diff --git a/rxjava-core/src/main/java/org/rx/functions/Functions.java b/rxjava-core/src/main/java/org/rx/functions/Functions.java
index 8ad1949745..6afaef4059 100644
--- a/rxjava-core/src/main/java/org/rx/functions/Functions.java
+++ b/rxjava-core/src/main/java/org/rx/functions/Functions.java
@@ -1,12 +1,12 @@
 /**
  * Copyright 2013 Netflix, Inc.
- *
+ * 
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -56,8 +56,13 @@ private static void loadLanguageAdaptor(String name) {
         }
     }
 
-    public static void registerLanguageAdaptor(Class<?> functionClass, FunctionLanguageAdaptor adaptor) {
-        languageAdaptors.put(functionClass, adaptor);
+    public static void registerLanguageAdaptor(Class<?>[] functionClasses, FunctionLanguageAdaptor adaptor) {
+        for (Class<?> functionClass : functionClasses) {
+            if (functionClass.getPackage().getName().startsWith("java.")) {
+                throw new IllegalArgumentException("FunctionLanguageAdaptor implementations can not specify java.lang.* classes.");
+            }
+            languageAdaptors.put(functionClass, adaptor);
+        }
     }
 
     public static void removeLanguageAdaptor(Class<?> functionClass) {