diff --git a/test/test_mongos_load_balancing.py b/test/test_mongos_load_balancing.py
index b939abeb5..aface3dae 100644
--- a/test/test_mongos_load_balancing.py
+++ b/test/test_mongos_load_balancing.py
@@ -149,20 +149,20 @@ class TestMongosLoadBalancing(MockClientTest):
                          writable_addresses(topology))
 
         # No error
-        client.db.collection.find_one()
+        client.admin.command('ismaster')
 
         client = connected(self.mock_client(localThresholdMS=0))
         self.assertEqual(0, client.local_threshold_ms)
         # No error
-        client.db.collection.find_one()
+        client.db.command('ismaster')
         # Our chosen mongos goes down.
         client.kill_host('%s:%s' % next(iter(client.nodes)))
         try:
-            client.db.collection.find_one()
+            client.db.command('ismaster')
         except:
             pass
         # No error
-        client.db.collection.find_one()
+        client.db.command('ismaster')
 
     def test_load_balancing(self):
         # Although the server selection JSON tests already prove that
diff --git a/test/test_read_preferences.py b/test/test_read_preferences.py
index f12818c1d..8bc6d6515 100644
--- a/test/test_read_preferences.py
+++ b/test/test_read_preferences.py
@@ -44,7 +44,7 @@ from test import (SkipTest,
                   unittest,
                   db_user,
                   db_pwd)
-from test.utils import single_client, one, wait_until, rs_client
+from test.utils import connected, single_client, one, wait_until, rs_client
 from test.version import Version
 
 
@@ -220,7 +220,11 @@ class TestReadPreferences(TestReadPreferencesBase):
         for ping_time, host in zip(ping_times, self.client.nodes):
             ServerDescription._host_to_round_trip_time[host] = ping_time
         try:
-            client = rs_client(readPreference='nearest', localThresholdMS=0)
+            client = connected(
+                rs_client(readPreference='nearest', localThresholdMS=0))
+            wait_until(
+                lambda: client.nodes == self.client.nodes,
+                "discovered all nodes")
             host = self.read_from_which_host(client)
             for _ in range(5):
                 self.assertEqual(host, self.read_from_which_host(client))