diff --git a/lib/bgcalc/freqs/storage.py b/lib/bgcalc/freqs/storage.py
index 88e0a86371..d03fb574b3 100644
--- a/lib/bgcalc/freqs/storage.py
+++ b/lib/bgcalc/freqs/storage.py
@@ -102,7 +102,7 @@ async def wrapper(args: FreqCalcArgs) -> FreqCalcResult:
         data, cache_path = await find_cached_result(args)
         if data is None:
             data: FreqCalcResult = await func(args)
-            async with aiofiles.open(cache_path, 'w') as fw, AsyncBatchWriter(fw, 100) as bw:
+            async with AsyncBatchWriter(cache_path, 'w', 100) as bw:
                 common_md = CommonMetadata(num_blocks=len(data.freqs), conc_size=data.conc_size)
                 await bw.write(json.dumps(common_md.to_dict()) + '\n')
                 for freq in data.freqs:
diff --git a/lib/bgcalc/keywords/__init__.py b/lib/bgcalc/keywords/__init__.py
index f8f980ab61..30d7869b17 100644
--- a/lib/bgcalc/keywords/__init__.py
+++ b/lib/bgcalc/keywords/__init__.py
@@ -108,7 +108,7 @@ async def wrapper(corp: KCorpus, ref_corp: KCorpus, args: KeywordsFormArgs, max_
             ans = await f(corp, ref_corp, args, max_items)
             # ans = sorted(ans, key=lambda x: x[1], reverse=True)
             num_lines = len(ans)
-            async with aiofiles.open(path, 'w') as fw, AsyncBatchWriter(fw, 100) as bw:
+            async with AsyncBatchWriter(path, 'w', 100) as bw:
                 await bw.write(json.dumps(dict(total=num_lines)) + '\n')
                 for item in ans:
                     await bw.write(item.to_json() + '\n')
diff --git a/lib/bgcalc/wordlist/__init__.py b/lib/bgcalc/wordlist/__init__.py
index a4577c84f1..1a29aa7e7e 100644
--- a/lib/bgcalc/wordlist/__init__.py
+++ b/lib/bgcalc/wordlist/__init__.py
@@ -77,7 +77,7 @@ async def wrapper(corp: AbstractKCorpus, args: WordlistFormArgs, max_items: int)
             ans = await f(corp, args, sys.maxsize)
             ans = sorted(ans, key=lambda x: x[1], reverse=True)
             num_lines = len(ans)
-            async with aiofiles.open(path, 'w') as fw, AsyncBatchWriter(fw, 100) as bw:
+            async with AsyncBatchWriter(path, 'w', 100) as bw:
                 await bw.write(json.dumps(dict(total=num_lines)) + '\n')
                 for item in ans:
                     await bw.write(json.dumps(item) + '\n')
diff --git a/lib/plugins/default_subcmixer/__init__.py b/lib/plugins/default_subcmixer/__init__.py
index 17b775412b..4050040ee9 100644
--- a/lib/plugins/default_subcmixer/__init__.py
+++ b/lib/plugins/default_subcmixer/__init__.py
@@ -20,7 +20,6 @@
 from collections import defaultdict
 from typing import Any, Dict, List
 
-import aiofiles
 import plugins
 import ujson as json
 from action.control import http_action
@@ -75,7 +74,7 @@ async def subcmixer_create_subcorpus(amodel: CorpusActionModel, req: KRequest, r
         struct_indices = sorted([int(x) for x in req.form.get('ids').split(',')])
         id_attr = req.form.get('idAttr').split('.')
         attr = amodel.corp.get_struct(id_attr[0])
-        async with aiofiles.open(os.path.join(amodel.subcpath, subc_id.data_path), 'wb') as fw, AsyncBatchWriter(fw, 100) as bw:
+        async with AsyncBatchWriter(os.path.join(amodel.subcpath, subc_id.data_path), 'wb', 100) as bw:
             for idx in struct_indices:
                 await bw.write(struct.pack('<q', attr.beg(idx)))
                 await bw.write(struct.pack('<q', attr.end(idx)))
diff --git a/lib/plugins/masm_live_attributes/doclist/writer.py b/lib/plugins/masm_live_attributes/doclist/writer.py
index 74ac9ca734..8d92ae8b14 100644
--- a/lib/plugins/masm_live_attributes/doclist/writer.py
+++ b/lib/plugins/masm_live_attributes/doclist/writer.py
@@ -48,7 +48,7 @@ async def export_xml(data: List[DocListItem], target_path: str) -> bool:
 async def export_jsonl(data: List[DocListItem], target_path: str) -> bool:
     if len(data) == 0:
         return False
-    async with aiofiles.open(target_path, 'w') as fw, AsyncBatchWriter(fw, 100) as bw:
+    async with AsyncBatchWriter(target_path, 'w', 100) as bw:
         for item in data:
             await bw.write(json.dumps(item.to_dict()) + "\n")
         return True
diff --git a/lib/plugins/masm_subcmixer/__init__.py b/lib/plugins/masm_subcmixer/__init__.py
index 9734ca58a5..c13b391266 100644
--- a/lib/plugins/masm_subcmixer/__init__.py
+++ b/lib/plugins/masm_subcmixer/__init__.py
@@ -21,7 +21,6 @@
 from dataclasses import dataclass
 from typing import List, Optional
 
-import aiofiles
 import aiohttp
 import plugins
 import ujson as json
@@ -79,7 +78,7 @@ async def subcmixer_create_subcorpus(amodel: CorpusActionModel, req: KRequest, r
         struct_idxs = sorted(attr.str2id(sid) for sid in struct_ids)
 
         subc_id = await create_new_subc_ident(amodel.subcpath, amodel.corp.corpname)
-        async with aiofiles.open(os.path.join(amodel.subcpath, subc_id.data_path), 'wb') as fw, AsyncBatchWriter(fw, 100) as bw:
+        async with AsyncBatchWriter(os.path.join(amodel.subcpath, subc_id.data_path), 'wb', 100) as bw:
             for idx in struct_idxs:
                 await bw.write(struct.pack('<q', mstruct.beg(idx)))
                 await bw.write(struct.pack('<q', mstruct.end(idx)))
diff --git a/lib/plugins/mysql_subc_storage/__init__.py b/lib/plugins/mysql_subc_storage/__init__.py
index e9f546c4d3..2d7922b538 100644
--- a/lib/plugins/mysql_subc_storage/__init__.py
+++ b/lib/plugins/mysql_subc_storage/__init__.py
@@ -21,7 +21,6 @@
 from datetime import datetime
 from typing import Any, Dict, List, Optional, Union
 
-import aiofiles
 import plugins
 import ujson as json
 from action.argmapping.subcorpus import (
@@ -161,7 +160,7 @@ async def create_preflight(self, subc_root_dir, corpname):
             new ID of the subcorpus
         """
         subc_id = await create_new_subc_ident(subc_root_dir, corpname)
-        async with aiofiles.open(os.path.join(subc_root_dir, subc_id.data_path), 'wb') as fw, AsyncBatchWriter(fw, 100) as bw:
+        async with AsyncBatchWriter(os.path.join(subc_root_dir, subc_id.data_path), 'wb', 100) as bw:
             await bw.write(struct.pack('<q', 0))
             await bw.write(struct.pack('<q', self.preflight_subcorpus_size))
         subcname = f'{corpname}-preflight'
diff --git a/lib/util.py b/lib/util.py
index d7d9e8b56c..36f27c1c19 100644
--- a/lib/util.py
+++ b/lib/util.py
@@ -3,6 +3,8 @@
 from functools import partial, wraps
 from typing import AsyncIterator, TypeVar
 
+import aiofiles
+
 T = TypeVar('T')
 
 
@@ -50,8 +52,10 @@ def int2chash(hex_num: int, length: int) -> str:
 
 
 class AsyncBatchWriter(AsyncContextDecorator):
-    def __init__(self, f, batch_size: int):
-        self.f = f
+    def __init__(self, filename: str, mode: str, batch_size: int):
+        self.filename = filename
+        self.mode = mode
+        self.f = None
         self.batch_size = batch_size
         self.lines = []
 
@@ -65,8 +69,10 @@ async def flush(self):
         self.lines = []
 
     async def __aenter__(self):
+        self.f = await aiofiles.open(self.filename, self.mode).__aenter__()
         return self
 
     async def __aexit__(self, *exc):
         await self.flush()
+        self.f.close()
         return False