diff --git a/chat_archiver/chat_archiver/main.py b/chat_archiver/chat_archiver/main.py
index 7c7ab56..0dd2edb 100644
--- a/chat_archiver/chat_archiver/main.py
+++ b/chat_archiver/chat_archiver/main.py
@@ -13,12 +13,11 @@ from calendar import timegm
 from collections import defaultdict
 from datetime import datetime
 from itertools import count
-from uuid import uuid4
 
 import gevent.event
 import gevent.queue
 
-from common import ensure_directory, listdir, rename
+from common import atomic_write, listdir
 from common.chat import BATCH_INTERVAL, format_batch, get_batch_files, merge_messages
 
 from girc import Client
@@ -275,14 +274,6 @@ class Archiver(object):
 		self.client.stop()
 
 
-def atomic_write(filepath, content):
-	temp_path = "{}.{}.temp".format(filepath, uuid4())
-	ensure_directory(filepath)
-	with open(temp_path, 'wb') as f:
-		f.write(content)
-	rename(temp_path, filepath)
-
-
 _EMOTES_RUNNING = {} # map (base_dir, emote id, theme, scale) -> in-progress greenlet fetching that path
 def ensure_emotes(base_dir, emote_ids):
 	"""Tries to download given emote from twitch if it doesn't already exist.
diff --git a/common/common/__init__.py b/common/common/__init__.py
index 8f288c2..616d5b1 100644
--- a/common/common/__init__.py
+++ b/common/common/__init__.py
@@ -6,6 +6,7 @@ import logging
 import os
 import random
 from signal import SIGTERM
+from uuid import uuid4
 
 import gevent.event
 
@@ -128,6 +129,21 @@ def writeall(write, value):
 		value = value[n:]
 
 
+def atomic_write(filepath, content):
+	"""Writes content to filepath atomically, ie. replacing the file in one step
+	without potential for partial write. content may be str or bytes.
+	If the file already exists, it will silently do nothing as it is assumed a given
+	filename can only ever contain the same content.
+	"""
+	if isinstance(content, str):
+		content = content.encode("utf-8")
+	temp_path = "{}.{}.temp".format(filepath, uuid4())
+	ensure_directory(filepath)
+	with open(temp_path, 'wb') as f:
+		writeall(f.write, content)
+	rename(temp_path, filepath)
+
+
 def serve_with_graceful_shutdown(server, stop_timeout=20):
 	"""Takes a gevent.WSGIServer and serves forever until SIGTERM is received,
 	or the server errors. This is slightly tricky to do due to race conditions