diff --git a/faust/__init__.py b/faust/__init__.py
index d5febf348..938e50aac 100644
--- a/faust/__init__.py
+++ b/faust/__init__.py
@@ -24,7 +24,7 @@
 
 from typing import Any, Mapping, NamedTuple, Optional, Sequence, Tuple
 
-__version__ = '1.13.0'
+__version__ = '1.13.1'
 __author__ = 'Robinhood Markets, Inc.'
 __contact__ = 'contact@fauststream.com'
 __homepage__ = 'http://faust.readthedocs.io/'
diff --git a/faust/transport/consumer.py b/faust/transport/consumer.py
index 87d9204b3..1a27299c3 100644
--- a/faust/transport/consumer.py
+++ b/faust/transport/consumer.py
@@ -78,6 +78,7 @@
 from mode.utils.text import pluralize
 from mode.utils.times import Seconds
 from faust.exceptions import ProducerSendError
+from intervaltree import IntervalTree
 from faust.types import AppT, ConsumerMessage, Message, RecordMetadata, TP
 from faust.types.core import HeadersArg
 from faust.types.transports import (
@@ -430,7 +431,7 @@ def __init__(self,
         self.commit_livelock_soft_timeout = (
             commit_livelock_soft_timeout or
             self.app.conf.broker_commit_livelock_soft_timeout)
-        self._gap = defaultdict(list)
+        self._gap = defaultdict(IntervalTree)
         self._acked = defaultdict(list)
         self._acked_index = defaultdict(set)
         self._read_offset = defaultdict(lambda: None)
@@ -975,13 +976,22 @@ def _new_offset(self, tp: TP) -> Optional[int]:
         # the return value will be: 36
         if acked:
             max_offset = max(acked)
-            gap_for_tp = self._gap[tp]
+            gap_for_tp: IntervalTree = self._gap[tp]
             if gap_for_tp:
-                gap_index = next((i for i, x in enumerate(gap_for_tp)
-                                  if x > max_offset), len(gap_for_tp))
-                gaps = gap_for_tp[:gap_index]
-                acked.extend(gaps)
-                gap_for_tp[:gap_index] = []
+                # find all the ranges up to the max of acked, add them in to acked,
+                 # and chop them off the gap.
+                 candidates = gap_for_tp.overlap(0, max_offset)
+                 # note: merge_overlaps will sort the intervaltree and will ensure that
+                 # the intervals left over don't overlap each other. So can sort by their
+                 # start without worrying about ends overlapping.
+                 sorted_candidates = sorted(candidates, key=lambda x: x.begin)
+                 if sorted_candidates:
+                     stuff_to_add = []
+                     for entry in sorted_candidates:
+                         stuff_to_add.extend(range(entry.begin, entry.end))
+                     new_max_offset = max(stuff_to_add[-1], max_offset + 1)
+                     acked.extend(stuff_to_add)
+                     gap_for_tp.chop(0, new_max_offset)
             acked.sort()
             # Note: acked is always kept sorted.
             # find first list of consecutive numbers
@@ -997,12 +1007,18 @@ async def on_task_error(self, exc: BaseException) -> None:
         """Call when processing a message failed."""
         await self.commit()
 
-    def _add_gap(self, tp: TP, offset_from: int, offset_to: int) -> None:
+    async def _add_gap(self, tp: TP, offset_from: int, offset_to: int) -> None:
         committed = self._committed_offset[tp]
         gap_for_tp = self._gap[tp]
-        for offset in range(offset_from, offset_to):
-            if committed is None or offset > committed:
-                gap_for_tp.append(offset)
+        if committed is not None:
+             offset_from = max(offset_from, committed + 1)
+         # intervaltree intervals exclude the end
+         if offset_from <= offset_to:
+             gap_for_tp.addi(offset_from, offset_to + 1)
+             # sleep 0 to allow other coroutines to get some loop time
+             # for example, to answer health checks while building the gap
+             await asyncio.sleep(0)
+             gap_for_tp.merge_overlaps()
 
     async def _drain_messages(
             self, fetcher: ServiceT) -> None:  # pragma: no cover
@@ -1050,7 +1066,7 @@ async def _drain_messages(
                             if gap > 1 and r_offset:
                                 acks_enabled = acks_enabled_for(message.topic)
                                 if acks_enabled:
-                                    self._add_gap(tp, r_offset + 1, offset)
+                                    await self._add_gap(tp, r_offset + 1, offset)
                             if commit_every is not None:
                                 if self._n_acked >= commit_every:
                                     self._n_acked = 0
diff --git a/requirements/dist.txt b/requirements/dist.txt
index f41b125b9..e37f8b7db 100644
--- a/requirements/dist.txt
+++ b/requirements/dist.txt
@@ -12,3 +12,4 @@ tox>=2.3.1
 twine
 vulture
 wheel>=0.29.0
+intervaltree
\ No newline at end of file