diff --git a/kafka/consumer/fetcher.py b/kafka/consumer/fetcher.py
index d4551a57d..c8e44372a 100644
--- a/kafka/consumer/fetcher.py
+++ b/kafka/consumer/fetcher.py
@@ -219,7 +219,8 @@ def offsets_by_times(self, timestamps, timeout_ms=None):
         Raises:
             KafkaTimeoutError if timeout_ms provided
         """
-        offsets = self._manager.run(self._fetch_offsets_by_times_async, timestamps, timeout_ms)
+        with self._client._lock:
+            offsets = self._manager.run(self._fetch_offsets_by_times_async, timestamps, timeout_ms)
         for tp in timestamps:
             if tp not in offsets:
                 offsets[tp] = None
@@ -344,7 +345,8 @@ def beginning_or_end_offset(self, partitions, timestamp, timeout_ms=None):
             KafkaTimeoutError if timeout_ms provided.
         """
         timestamps = dict([(tp, timestamp) for tp in partitions])
-        offsets = self._manager.run(self._fetch_offsets_by_times_async, timestamps, timeout_ms)
+        with self._client._lock:
+            offsets = self._manager.run(self._fetch_offsets_by_times_async, timestamps, timeout_ms)
         for tp in timestamps:
             offsets[tp] = offsets[tp].offset
         return offsets