diff --git a/contrib/crawl.py b/contrib/crawl.py
index cc88b77..1c1f3fe 100755
--- a/contrib/crawl.py
+++ b/contrib/crawl.py
@@ -155,14 +155,14 @@ def crawl(router):
 		try:
 			if router["system"]["uptime"] > router_update["system"]["uptime"]:
 				events.append({
-					"time": datetime.datetime.utcnow(),
+					"time": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
 					"type": "reboot",
 				})
 		except:
 			pass
 		if router["status"] != status:
 			events.append({
-				"time": datetime.datetime.utcnow(),
+				"time": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
 				"type": status,
 			})
 		db.routers.update_one({"_id": router["_id"]}, {"$push": {"events": {
diff --git a/contrib/import_from_netmon.py b/contrib/import_from_netmon.py
index 398b503..3040a8e 100755
--- a/contrib/import_from_netmon.py
+++ b/contrib/import_from_netmon.py
@@ -79,7 +79,7 @@ for r in tree.xpath("/netmon_response/routerlist/router"):
 				"ipv6_fe80_addr": netif_ip
 			}]
 
-		router["created"] = datetime.datetime.utcnow()
+		router["created"] = datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc)
 		router["status"] = "unknown"
 
 		db.routers.insert_one(router)
diff --git a/ffmap/dbtools.py b/ffmap/dbtools.py
index bbff1ca..c93bf7e 100644
--- a/ffmap/dbtools.py
+++ b/ffmap/dbtools.py
@@ -9,7 +9,7 @@ class FreifunkDB(object):
 	@classmethod
 	def handle(cls):
 		if not cls.client:
-			cls.client = MongoClient()
+			cls.client = MongoClient(tz_aware=True)
 		if not cls.db:
 			cls.db = cls.client.freifunk
 		return cls.db
diff --git a/ffmap/routertools.py b/ffmap/routertools.py
index 8dad92c..837d497 100644
--- a/ffmap/routertools.py
+++ b/ffmap/routertools.py
@@ -37,7 +37,7 @@ def import_nodewatcher_xml(mac, xml):
 			router_info = netmon_fetch_router_info(mac)
 			if router_info:
 				events.append({
-					"time": datetime.datetime.utcnow(),
+					"time": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
 					"type": "netmon",
 					"comment": "Fetched metadata from netmon",
 				})
@@ -64,11 +64,11 @@ def import_nodewatcher_xml(mac, xml):
 			}})
 		else:
 			# insert new router
-			router_update["created"] = datetime.datetime.utcnow()
+			router_update["created"] = datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc)
 			router_update["stats"] = []
 			events = [] # don't fire sub-events of created events
 			router_update["events"] = [{
-				"time": datetime.datetime.utcnow(),
+				"time": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
 				"type": "created",
 			}]
 			router_id = db.routers.insert_one(router_update).inserted_id
@@ -84,14 +84,14 @@ def import_nodewatcher_xml(mac, xml):
 		with suppress(KeyError, TypeError):
 			if router["system"]["uptime"] > router_update["system"]["uptime"]:
 				events.append({
-					"time": datetime.datetime.utcnow(),
+					"time": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
 					"type": "reboot",
 				})
 
 		with suppress(KeyError, TypeError):
 			if router["software"]["firmware"] != router_update["software"]["firmware"]:
 				events.append({
-					"time": datetime.datetime.utcnow(),
+					"time": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
 					"type": "update",
 					"comment": "%s -> %s" % (router["software"]["firmware"], router_update["software"]["firmware"]),
 				})
@@ -99,7 +99,7 @@ def import_nodewatcher_xml(mac, xml):
 		with suppress(KeyError, TypeError):
 			if router["hostname"] != router_update["hostname"]:
 				events.append({
-					"time": datetime.datetime.utcnow(),
+					"time": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
 					"type": "hostname",
 					"comment": "%s -> %s" % (router["hostname"], router_update["hostname"]),
 				})
@@ -107,7 +107,7 @@ def import_nodewatcher_xml(mac, xml):
 		with suppress(KeyError, TypeError):
 			if router["hood"] != router_update["hood"]:
 				events.append({
-					"time": datetime.datetime.utcnow(),
+					"time": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
 					"type": "hood",
 					"comment": "%s -> %s" % (router["hood"], router_update["hood"]),
 				})
@@ -115,7 +115,7 @@ def import_nodewatcher_xml(mac, xml):
 		with suppress(KeyError, TypeError):
 			if router["status"] != status:
 				events.append({
-					"time": datetime.datetime.utcnow(),
+					"time": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
 					"type": status,
 				})
 
@@ -127,12 +127,12 @@ def import_nodewatcher_xml(mac, xml):
 
 def detect_offline_routers():
 	db.routers.update_many({
-		"last_contact": {"$lt": datetime.datetime.utcnow() - datetime.timedelta(minutes=CONFIG["offline_threshold_minutes"])},
+		"last_contact": {"$lt": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc) - datetime.timedelta(minutes=CONFIG["offline_threshold_minutes"])},
 		"status": {"$ne": "offline"}
 	}, {
 		"$set": {"status": "offline", "system.clients": 0},
 		"$push": {"events": {
-			"time": datetime.datetime.utcnow(),
+			"time": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
 			"type": "offline"
 		}
 	}})
@@ -150,7 +150,7 @@ def new_router_stats(router, router_update):
 			with suppress(KeyError):
 				neighbours[neighbour["mac"]] = neighbour["quality"]
 		return [{
-			"time": datetime.datetime.utcnow(),
+			"time": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
 			"netifs": netifs,
 			"neighbours": neighbours,
 			"memory": router_update["system"]["memory"],
@@ -190,7 +190,7 @@ def parse_nodewatcher_xml(xml):
 		router_update = {
 			"status": tree.xpath("/data/system_data/status/text()")[0],
 			"hostname": tree.xpath("/data/system_data/hostname/text()")[0],
-			"last_contact": datetime.datetime.utcnow(),
+			"last_contact": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
 			"neighbours": [],
 			"netifs": [],
 			"system": {
diff --git a/ffmap/stattools.py b/ffmap/stattools.py
index 15ac978..a7d51ef 100644
--- a/ffmap/stattools.py
+++ b/ffmap/stattools.py
@@ -75,7 +75,7 @@ def hoods_sum():
 
 def record_global_stats():
 	db.stats.insert_one({
-		"time": datetime.datetime.utcnow(),
+		"time": datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc),
 		"router_status": router_status(),
 		"total_clients": total_clients()
 	})
diff --git a/ffmap/web/filters.py b/ffmap/web/filters.py
index 276f58b..882333f 100644
--- a/ffmap/web/filters.py
+++ b/ffmap/web/filters.py
@@ -29,7 +29,7 @@ def neighbour_color(quality):
 
 @filters.app_template_filter('utc2local')
 def utc2local(dt):
-	return dt.replace(tzinfo=tz.tzutc()).astimezone(tz.tzlocal())
+	return dt.astimezone(tz.tzlocal())
 
 @filters.app_template_filter('format_dt')
 def format_dt(dt):
@@ -45,7 +45,7 @@ def dt2jstimestamp(dt):
 
 @filters.app_template_filter('format_dt_ago')
 def format_dt_ago(dt):
-	diff = datetime.datetime.utcnow() - dt
+	diff = datetime.datetime.utcnow().replace(tzinfo=datetime.timezone.utc) - dt
 	s = diff.seconds
 	if diff.days > 1:
 		return '%i days ago' % diff.days