diff --git a/src/main/java/org/whispersystems/textsecuregcm/controllers/MessageController.java b/src/main/java/org/whispersystems/textsecuregcm/controllers/MessageController.java
index bf854326e..d5972fde6 100644
--- a/src/main/java/org/whispersystems/textsecuregcm/controllers/MessageController.java
+++ b/src/main/java/org/whispersystems/textsecuregcm/controllers/MessageController.java
@@ -26,7 +26,7 @@ import org.whispersystems.textsecuregcm.entities.IncomingMessage;
 import org.whispersystems.textsecuregcm.entities.IncomingMessageList;
 import org.whispersystems.textsecuregcm.entities.MessageProtos.OutgoingMessageSignal;
 import org.whispersystems.textsecuregcm.entities.MessageResponse;
-import org.whispersystems.textsecuregcm.entities.MissingDevices;
+import org.whispersystems.textsecuregcm.entities.MismatchedDevices;
 import org.whispersystems.textsecuregcm.federation.FederatedClient;
 import org.whispersystems.textsecuregcm.federation.FederatedClientManager;
 import org.whispersystems.textsecuregcm.federation.NoSuchPeerException;
@@ -92,15 +92,15 @@ public class MessageController {
       else                             sendRelayMessage(source, destinationName, messages);
     } catch (NoSuchUserException e) {
       throw new WebApplicationException(Response.status(404).build());
-    } catch (MissingDevicesException e) {
+    } catch (MismatchedDevicesException e) {
       throw new WebApplicationException(Response.status(409)
-                                                .entity(new MissingDevices(e.getMissingDevices()))
+                                                .entity(new MismatchedDevices(e.getMissingDevices(),
+                                                                              e.getExtraDevices()))
                                                 .build());
     }
   }
 
   @Timed
-  @Path("/")
   @POST
   @Consumes(MediaType.APPLICATION_JSON)
   @Produces(MediaType.APPLICATION_JSON)
@@ -123,7 +123,7 @@ public class MessageController {
   private void sendLocalMessage(Account source,
                                 String destinationName,
                                 IncomingMessageList messages)
-      throws NoSuchUserException, MissingDevicesException, IOException
+      throws NoSuchUserException, MismatchedDevicesException, IOException
   {
     Account destination = getDestinationAccount(destinationName);
 
@@ -196,23 +196,34 @@ public class MessageController {
   }
 
   private void validateCompleteDeviceList(Account account, List<IncomingMessage> messages)
-      throws MissingDevicesException
+      throws MismatchedDevicesException
   {
-    Set<Long> destinationDeviceIds = new HashSet<>();
-    List<Long> missingDeviceIds    = new LinkedList<>();
+    Set<Long> messageDeviceIds = new HashSet<>();
+    Set<Long> accountDeviceIds = new HashSet<>();
+
+    List<Long> missingDeviceIds = new LinkedList<>();
+    List<Long> extraDeviceIds   = new LinkedList<>();
 
     for (IncomingMessage message : messages) {
-      destinationDeviceIds.add(message.getDestinationDeviceId());
+      messageDeviceIds.add(message.getDestinationDeviceId());
     }
 
     for (Device device : account.getDevices()) {
-      if (!destinationDeviceIds.contains(device.getId())) {
+      accountDeviceIds.add(device.getId());
+
+      if (!messageDeviceIds.contains(device.getId())) {
         missingDeviceIds.add(device.getId());
       }
     }
 
-    if (!missingDeviceIds.isEmpty()) {
-      throw new MissingDevicesException(missingDeviceIds);
+    for (IncomingMessage message : messages) {
+      if (!accountDeviceIds.contains(message.getDestinationDeviceId())) {
+        extraDeviceIds.add(message.getDestinationDeviceId());
+      }
+    }
+
+    if (!missingDeviceIds.isEmpty() || !extraDeviceIds.isEmpty()) {
+      throw new MismatchedDevicesException(missingDeviceIds, extraDeviceIds);
     }
   }
 
diff --git a/src/main/java/org/whispersystems/textsecuregcm/controllers/MismatchedDevicesException.java b/src/main/java/org/whispersystems/textsecuregcm/controllers/MismatchedDevicesException.java
new file mode 100644
index 000000000..3748b638c
--- /dev/null
+++ b/src/main/java/org/whispersystems/textsecuregcm/controllers/MismatchedDevicesException.java
@@ -0,0 +1,23 @@
+package org.whispersystems.textsecuregcm.controllers;
+
+import java.util.List;
+import java.util.Set;
+
+public class MismatchedDevicesException extends Exception {
+
+  private final List<Long> missingDevices;
+  private final List<Long> extraDevices;
+
+  public MismatchedDevicesException(List<Long> missingDevices, List<Long> extraDevices) {
+    this.missingDevices = missingDevices;
+    this.extraDevices   = extraDevices;
+  }
+
+  public List<Long> getMissingDevices() {
+    return missingDevices;
+  }
+
+  public List<Long> getExtraDevices() {
+    return extraDevices;
+  }
+}
diff --git a/src/main/java/org/whispersystems/textsecuregcm/controllers/MissingDevicesException.java b/src/main/java/org/whispersystems/textsecuregcm/controllers/MissingDevicesException.java
deleted file mode 100644
index 513ad50d4..000000000
--- a/src/main/java/org/whispersystems/textsecuregcm/controllers/MissingDevicesException.java
+++ /dev/null
@@ -1,16 +0,0 @@
-package org.whispersystems.textsecuregcm.controllers;
-
-import java.util.List;
-import java.util.Set;
-
-public class MissingDevicesException extends Exception {
-  private final List<Long> missingDevices;
-
-  public MissingDevicesException(List<Long> missingDevices) {
-    this.missingDevices = missingDevices;
-  }
-
-  public List<Long> getMissingDevices() {
-    return missingDevices;
-  }
-}
diff --git a/src/main/java/org/whispersystems/textsecuregcm/entities/MissingDevices.java b/src/main/java/org/whispersystems/textsecuregcm/entities/MismatchedDevices.java
similarity index 53%
rename from src/main/java/org/whispersystems/textsecuregcm/entities/MissingDevices.java
rename to src/main/java/org/whispersystems/textsecuregcm/entities/MismatchedDevices.java
index e9c10e1c1..20df30c1d 100644
--- a/src/main/java/org/whispersystems/textsecuregcm/entities/MissingDevices.java
+++ b/src/main/java/org/whispersystems/textsecuregcm/entities/MismatchedDevices.java
@@ -4,13 +4,17 @@ import com.fasterxml.jackson.annotation.JsonProperty;
 
 import java.util.List;
 
-public class MissingDevices {
+public class MismatchedDevices {
 
   @JsonProperty
   public List<Long> missingDevices;
 
-  public MissingDevices(List<Long> missingDevices) {
+  @JsonProperty
+  public List<Long> extraDevices;
+
+  public MismatchedDevices(List<Long> missingDevices, List<Long> extraDevices) {
     this.missingDevices = missingDevices;
+    this.extraDevices   = extraDevices;
   }
 
 }
diff --git a/src/main/java/org/whispersystems/textsecuregcm/storage/AccountsManager.java b/src/main/java/org/whispersystems/textsecuregcm/storage/AccountsManager.java
index 46eb87257..345569f7f 100644
--- a/src/main/java/org/whispersystems/textsecuregcm/storage/AccountsManager.java
+++ b/src/main/java/org/whispersystems/textsecuregcm/storage/AccountsManager.java
@@ -19,19 +19,11 @@ package org.whispersystems.textsecuregcm.storage;
 
 import com.google.common.base.Optional;
 import net.spy.memcached.MemcachedClient;
-import org.whispersystems.textsecuregcm.controllers.MissingDevicesException;
 import org.whispersystems.textsecuregcm.entities.ClientContact;
-import org.whispersystems.textsecuregcm.util.Pair;
 import org.whispersystems.textsecuregcm.util.Util;
-import sun.util.logging.resources.logging_zh_CN;
 
-import java.util.HashMap;
-import java.util.HashSet;
 import java.util.Iterator;
-import java.util.LinkedList;
 import java.util.List;
-import java.util.Map;
-import java.util.Set;
 
 public class AccountsManager {