diff --git a/python/plasma/plasma.py b/python/plasma/plasma.py
index e5e62d602..37b53fa0d 100644
--- a/python/plasma/plasma.py
+++ b/python/plasma/plasma.py
@@ -260,6 +260,8 @@ class PlasmaClient(object):
   def wait(self, object_ids, timeout=PLASMA_WAIT_TIMEOUT, num_returns=1):
     """Wait until num_returns objects in object_ids are ready.
 
+    Currently, the object ID arguments to wait must be unique.
+
     Args:
       object_ids (List[str]): List of object IDs to wait for.
       timeout (int): Return to the caller after timeout milliseconds.
@@ -269,6 +271,10 @@ class PlasmaClient(object):
       ready_ids, waiting_ids (List[str], List[str]): List of object IDs that
         are ready and list of object IDs we might still wait on respectively.
     """
+    # Check that the object ID arguments are unique. The plasma manager
+    # currently crashes if given duplicate object IDs.
+    if len(object_ids) != len(set(object_ids)):
+      raise Exception("Wait requires a list of unique object IDs.")
     ready_ids, waiting_ids = libplasma.wait(self.conn, object_ids, timeout, num_returns)
     return ready_ids, list(waiting_ids)
 
diff --git a/python/ray/worker.py b/python/ray/worker.py
index 8754f523d..8930e98ce 100644
--- a/python/ray/worker.py
+++ b/python/ray/worker.py
@@ -1421,7 +1421,7 @@ def wait(object_ids, num_returns=1, timeout=None, worker=global_worker):
 
   Args:
     object_ids (List[ObjectID]): List of object IDs for objects that may
-      or may not be ready.
+      or may not be ready. Note that these IDs must be unique.
     num_returns (int): The number of object IDs that should be returned.
     timeout (int): The maximum amount of time in milliseconds to wait before
       returning.
diff --git a/test/runtest.py b/test/runtest.py
index e357356bc..24aeff7a1 100644
--- a/test/runtest.py
+++ b/test/runtest.py
@@ -380,6 +380,10 @@ class APITest(unittest.TestCase):
     self.assertEqual(len(ready_ids), 1)
     self.assertEqual(len(remaining_ids), 3)
 
+    # Verify that calling wait with duplicate object IDs throws an exception.
+    x = ray.put(1)
+    self.assertRaises(Exception, lambda : ray.wait([x, x]))
+
     ray.worker.cleanup()
 
   def testMultipleWaitsAndGets(self):