diff --git a/extensions/multibindings/src/com/google/inject/multibindings/Multibinder.java b/extensions/multibindings/src/com/google/inject/multibindings/Multibinder.java
index 59fe82d..3b5284d 100644
--- a/extensions/multibindings/src/com/google/inject/multibindings/Multibinder.java
+++ b/extensions/multibindings/src/com/google/inject/multibindings/Multibinder.java
@@ -16,16 +16,13 @@
 
 package com.google.inject.multibindings;
 
+import static com.google.common.base.Predicates.equalTo;
+import static com.google.common.collect.Iterables.filter;
+import static com.google.common.collect.Iterables.getOnlyElement;
 import static com.google.inject.multibindings.Element.Type.MULTIBINDER;
 import static com.google.inject.name.Names.named;
 
-import java.lang.annotation.Annotation;
-import java.lang.reflect.Type;
-import java.util.Collections;
-import java.util.LinkedHashSet;
-import java.util.List;
-import java.util.Set;
-
+import com.google.common.base.Objects;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Lists;
@@ -50,6 +47,13 @@
 import com.google.inject.spi.Toolable;
 import com.google.inject.util.Types;
 
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Type;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
 /**
  * An API to bind multiple values separately, only to later inject them as a
  * complete collection. Multibinder is intended for use in your application's
@@ -323,14 +327,16 @@
     public Set<T> get() {
       checkConfiguration(isInitialized(), "Multibinder is not initialized");
 
-      Set<T> result = new LinkedHashSet<T>();
+      Map<T, Binding<T>> result = new LinkedHashMap<T, Binding<T>>();
       for (Binding<T> binding : bindings) {
         final T newValue = binding.getProvider().get();
         checkConfiguration(newValue != null, "Set injection failed due to null element");
-        checkConfiguration(result.add(newValue) || permitDuplicates,
-            "Set injection failed due to duplicated element \"%s\"", newValue);
+        Binding<T> duplicateBinding = result.put(newValue, binding);
+        if (!permitDuplicates && duplicateBinding != null) {
+          throw newDuplicateValuesException(result, binding, newValue, duplicateBinding);
+        }
       }
-      return Collections.unmodifiableSet(result);
+      return ImmutableSet.copyOf(result.keySet());
     }
     
     @SuppressWarnings("unchecked")
@@ -447,6 +453,35 @@
     throw new ConfigurationException(ImmutableSet.of(new Message(Errors.format(format, args))));
   }
 
+  private static <T> ConfigurationException newDuplicateValuesException(
+      Map<T, Binding<T>> existingBindings,
+      Binding<T> binding,
+      final T newValue,
+      Binding<T> duplicateBinding) {
+    T oldValue = getOnlyElement(filter(existingBindings.keySet(), equalTo(newValue)));
+    String oldString = oldValue.toString();
+    String newString = newValue.toString();
+    if (Objects.equal(oldString, newString)) {
+      // When the value strings match, just show the source of the bindings
+      return new ConfigurationException(ImmutableSet.of(new Message(Errors.format(
+          "Set injection failed due to duplicated element \"%s\""
+              + "\n    Bound at %s\n    Bound at %s",
+          newValue,
+          duplicateBinding.getSource(),
+          binding.getSource()))));
+    } else {
+      // When the value strings don't match, include them both as they may be useful for debugging
+      return new ConfigurationException(ImmutableSet.of(new Message(Errors.format(
+          "Set injection failed due to multiple elements comparing equal:"
+              + "\n    \"%s\"\n        bound at %s"
+              + "\n    \"%s\"\n        bound at %s",
+          oldValue,
+          duplicateBinding.getSource(),
+          newValue,
+          binding.getSource()))));
+    }
+  }
+
   static <T> T checkNotNull(T reference, String name) {
     if (reference != null) {
       return reference;
diff --git a/extensions/multibindings/test/com/google/inject/multibindings/MultibinderTest.java b/extensions/multibindings/test/com/google/inject/multibindings/MultibinderTest.java
index 4e1d3f1..28ed1ce 100644
--- a/extensions/multibindings/test/com/google/inject/multibindings/MultibinderTest.java
+++ b/extensions/multibindings/test/com/google/inject/multibindings/MultibinderTest.java
@@ -48,10 +48,14 @@
 import com.google.inject.spi.LinkedKeyBinding;
 import com.google.inject.util.Modules;
 import com.google.inject.util.Providers;
-import com.google.inject.util.Types;
 
 import junit.framework.TestCase;
 
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
 import java.lang.annotation.Annotation;
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
@@ -254,6 +258,32 @@
     }
   }
 
+  public void testMultibinderSetIsSerializable() throws IOException, ClassNotFoundException {
+    Injector injector = Guice.createInjector(new AbstractModule() {
+      protected void configure() {
+        Multibinder.newSetBinder(binder(), String.class)
+            .addBinding().toInstance("A");
+      }
+    });
+
+    Set<String> set = injector.getInstance(Key.get(setOfString));
+    ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
+    ObjectOutputStream objectOutputStream = new ObjectOutputStream(byteStream);
+    try {
+      objectOutputStream.writeObject(set);
+    } finally {
+      objectOutputStream.close();
+    }
+    ObjectInputStream objectInputStream = new ObjectInputStream(
+        new ByteArrayInputStream(byteStream.toByteArray()));
+    try {
+      Object setCopy = objectInputStream.readObject();
+      assertEquals(set, setCopy);
+    } finally {
+      objectInputStream.close();
+    }
+  }
+
   public void testMultibinderSetIsLazy() {
     Module module = new AbstractModule() {
       protected void configure() {
@@ -275,28 +305,94 @@
   }
 
   public void testMultibinderSetForbidsDuplicateElements() {
-    Module module = new AbstractModule() {
+    Module module1 = new AbstractModule() {
       protected void configure() {
         final Multibinder<String> multibinder = Multibinder.newSetBinder(binder(), String.class);
         multibinder.addBinding().toInstance("A");
+      }
+    };
+    Module module2 = new AbstractModule() {
+      protected void configure() {
+        final Multibinder<String> multibinder = Multibinder.newSetBinder(binder(), String.class);
         multibinder.addBinding().toInstance("A");
       }
     };
-    Injector injector = Guice.createInjector(module);
+    Injector injector = Guice.createInjector(module1, module2);
 
     try {
       injector.getInstance(Key.get(setOfString));
       fail();
-    } catch(ProvisionException expected) {
+    } catch (ProvisionException expected) {
       assertContains(expected.getMessage(),
-          "1) Set injection failed due to duplicated element \"A\"");
+          "1) Set injection failed due to duplicated element \"A\"",
+          "Bound at " + module1.getClass().getName(),
+          "Bound at " + module2.getClass().getName());
     }
 
     // But we can still visit the module!
-    assertSetVisitor(Key.get(setOfString), stringType, setOf(module), MODULE, false, 0,
+    assertSetVisitor(Key.get(setOfString), stringType, setOf(module1, module2), MODULE, false, 0,
         instance("A"), instance("A"));
   }
 
+  public void testMultibinderSetShowsBothElementsIfToStringDifferent() {
+    // A simple example of a type whose toString returns more information than its equals method
+    // considers.
+    class ValueType {
+      int a;
+      int b;
+      ValueType(int a, int b) {
+        this.a = a;
+        this.b = b;
+      }
+      @Override
+      public boolean equals(Object obj) {
+        return (obj instanceof ValueType) && (((ValueType) obj).a == a);
+      }
+      @Override
+      public int hashCode() {
+        return a;
+      }
+      @Override
+      public String toString() {
+        return String.format("ValueType(%d,%d)", a, b);
+      }
+    }
+    
+    Module module1 = new AbstractModule() {
+      protected void configure() {
+        final Multibinder<ValueType> multibinder =
+            Multibinder.newSetBinder(binder(), ValueType.class);
+        multibinder.addBinding().toInstance(new ValueType(1, 2));
+      }
+    };
+    Module module2 = new AbstractModule() {
+      protected void configure() {
+        final Multibinder<ValueType> multibinder =
+            Multibinder.newSetBinder(binder(), ValueType.class);
+        multibinder.addBinding().toInstance(new ValueType(1, 3));
+      }
+    };
+    Injector injector = Guice.createInjector(module1, module2);
+
+    TypeLiteral<ValueType> valueType = TypeLiteral.get(ValueType.class);
+    TypeLiteral<Set<ValueType>> setOfValueType = new TypeLiteral<Set<ValueType>>() {};
+    try {
+      injector.getInstance(Key.get(setOfValueType));
+      fail();
+    } catch (ProvisionException expected) {
+      assertContains(expected.getMessage(),
+          "1) Set injection failed due to multiple elements comparing equal:",
+          "\"ValueType(1,2)\"",
+          "bound at " + module1.getClass().getName(),
+          "\"ValueType(1,3)\"",
+          "bound at " + module2.getClass().getName());
+    }
+
+    // But we can still visit the module!
+    assertSetVisitor(Key.get(setOfValueType), valueType, setOf(module1, module2), MODULE, false, 0,
+        instance(new ValueType(1, 2)), instance(new ValueType(1, 3)));
+  }
+
   public void testMultibinderSetPermitDuplicateElements() {
     Module ab = new AbstractModule() {
       protected void configure() {