diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreImpl.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreImpl.java
index 577c8c42ea47..d16afbce4d5e 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreImpl.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreImpl.java
@@ -105,8 +105,18 @@ public Key allocateId(IncompleteKey key) {
     return DatastoreHelper.allocateId(this, key);
   }
 
+  private boolean verifyIncompleteKeyType(IncompleteKey... keys) {
+    for (IncompleteKey key : keys) {
+      if (key instanceof Key) {
+        return false;
+      }
+    }
+    return true;
+  }
+
   @Override
   public List<Key> allocateId(IncompleteKey... keys) {
+    Preconditions.checkArgument(verifyIncompleteKeyType(keys), "keys must be IncompleteKey instances");
     if (keys.length == 0) {
       return Collections.emptyList();
     }
@@ -123,7 +133,7 @@ public List<Key> allocateId(IncompleteKey... keys) {
     return keyList.build();
   }
 
-  com.google.datastore.v1.AllocateIdsResponse allocateIds(
+  private com.google.datastore.v1.AllocateIdsResponse allocateIds(
       final com.google.datastore.v1.AllocateIdsRequest requestPb) {
     try {
       return RetryHelper.runWithRetries(
diff --git a/google-cloud-datastore/src/test/java/com/google/cloud/datastore/DatastoreTest.java b/google-cloud-datastore/src/test/java/com/google/cloud/datastore/DatastoreTest.java
index 4e1c1fe68cd1..d4717e2ce150 100644
--- a/google-cloud-datastore/src/test/java/com/google/cloud/datastore/DatastoreTest.java
+++ b/google-cloud-datastore/src/test/java/com/google/cloud/datastore/DatastoreTest.java
@@ -688,9 +688,12 @@ public void testAllocateId() {
     assertNotEquals(key1, key2);
     assertEquals(Key.newBuilder(pk1, key2.getId()).build(), key2);
 
-    Key key3 = datastore.allocateId(key1);
-    assertNotEquals(key1, key3);
-    assertEquals(Key.newBuilder(pk1, key3.getId()).build(), key3);
+    try {
+      datastore.allocateId(key1);
+      fail("Expecting a failure");
+    } catch (IllegalArgumentException expected) {
+      assertEquals(expected.getMessage(), "keys must be IncompleteKey instances");
+    }
   }
 
   @Test
@@ -700,16 +703,20 @@ public void testAllocateIdArray() {
     IncompleteKey incompleteKey2 =
         keyFactory.setKind(KIND2).addAncestor(PathElement.of(KIND1, 10)).newKey();
     Key key3 = keyFactory.newKey("name");
-    Key key4 = keyFactory.newKey(1);
-    List<Key> result =
-        datastore.allocateId(incompleteKey1, incompleteKey2, key3, key4, incompleteKey1, key3);
-    assertEquals(6, result.size());
-    assertEquals(Key.newBuilder(incompleteKey1, result.get(0).getId()).build(), result.get(0));
-    assertEquals(Key.newBuilder(incompleteKey1, result.get(4).getId()).build(), result.get(4));
-    assertEquals(Key.newBuilder(incompleteKey2, result.get(1).getId()).build(), result.get(1));
-    assertEquals(Key.newBuilder(key3).setId(result.get(2).getId()).build(), result.get(2));
-    assertEquals(Key.newBuilder(key3).setId(result.get(5).getId()).build(), result.get(5));
-    assertEquals(Key.newBuilder(key4).setId(result.get(3).getId()).build(), result.get(3));
+    List<Key> result1 =
+            datastore.allocateId(incompleteKey1, incompleteKey2, incompleteKey1);
+    assertEquals(3, result1.size());
+    assertEquals(Key.newBuilder(incompleteKey1, result1.get(0).getId()).build(), result1.get(0));
+    assertEquals(Key.newBuilder(incompleteKey1, result1.get(2).getId()).build(), result1.get(2));
+    assertEquals(Key.newBuilder(incompleteKey2, result1.get(1).getId()).build(), result1.get(1));
+
+    try {
+      datastore.allocateId(incompleteKey1, incompleteKey2, key3);
+      fail("expecting a failure");
+    } catch(IllegalArgumentException expected) {
+        assertEquals(expected.getMessage(), "keys must be IncompleteKey instances");
+
+    }
   }
 
   @Test
diff --git a/google-cloud-datastore/src/test/java/com/google/cloud/datastore/it/ITDatastoreTest.java b/google-cloud-datastore/src/test/java/com/google/cloud/datastore/it/ITDatastoreTest.java
index a68175ccd6fc..16a1d24cc12d 100644
--- a/google-cloud-datastore/src/test/java/com/google/cloud/datastore/it/ITDatastoreTest.java
+++ b/google-cloud-datastore/src/test/java/com/google/cloud/datastore/it/ITDatastoreTest.java
@@ -517,10 +517,6 @@ public void testAllocateId() {
     Key key2 = DATASTORE.allocateId(pk1);
     assertNotEquals(key1, key2);
     assertEquals(Key.newBuilder(pk1, key2.getId()).build(), key2);
-
-    Key key3 = DATASTORE.allocateId(key1);
-    assertNotEquals(key1, key3);
-    assertEquals(Key.newBuilder(pk1, key3.getId()).build(), key3);
   }
 
   @Test
@@ -529,17 +525,12 @@ public void testAllocateIdArray() {
     IncompleteKey incompleteKey1 = keyFactory.newKey();
     IncompleteKey incompleteKey2 =
         keyFactory.setKind(KIND2).addAncestors(PathElement.of(KIND1, 10)).newKey();
-    Key key3 = keyFactory.newKey("name");
-    Key key4 = keyFactory.newKey(1);
     List<Key> result =
-        DATASTORE.allocateId(incompleteKey1, incompleteKey2, key3, key4, incompleteKey1, key3);
-    assertEquals(6, result.size());
+        DATASTORE.allocateId(incompleteKey1, incompleteKey2, incompleteKey1);
+    assertEquals(3, result.size());
     assertEquals(Key.newBuilder(incompleteKey1, result.get(0).getId()).build(), result.get(0));
-    assertEquals(Key.newBuilder(incompleteKey1, result.get(4).getId()).build(), result.get(4));
+    assertEquals(Key.newBuilder(incompleteKey1, result.get(2).getId()).build(), result.get(2));
     assertEquals(Key.newBuilder(incompleteKey2, result.get(1).getId()).build(), result.get(1));
-    assertEquals(Key.newBuilder(key3).setId(result.get(2).getId()).build(), result.get(2));
-    assertEquals(Key.newBuilder(key3).setId(result.get(5).getId()).build(), result.get(5));
-    assertEquals(Key.newBuilder(key4).setId(result.get(3).getId()).build(), result.get(3));
   }
 
   @Test