diff --git a/app/channels/presence_channel.rb b/app/channels/presence_channel.rb
index 3ad3bc9..249f6ff 100644
--- a/app/channels/presence_channel.rb
+++ b/app/channels/presence_channel.rb
@@ -22,6 +22,6 @@ class PresenceChannel < RoomChannel
     end
 
     def broadcast_read_room
-      ActionCable.server.broadcast "user_#{current_user.id}_reads", { room_id: membership.room_id, at: Time.current.to_fs(:epoch) }
+      ActionCable.server.broadcast "user_#{current_user.id}_reads", { room_id: membership.room_id, at: Time.current.to_f }
     end
 end
diff --git a/app/models/message/broadcasts.rb b/app/models/message/broadcasts.rb
index 7118f82..e3f8c00 100644
--- a/app/models/message/broadcasts.rb
+++ b/app/models/message/broadcasts.rb
@@ -13,7 +13,7 @@ module Message::Broadcasts
   # only the ones who still have it unread or are in it now: by the time this runs,
   # someone may have opened the room and moved on, and would see it marked unread again.
   def broadcast_unread_room
-    payload = ActiveSupport::JSON.encode(roomId: room.id, at: created_at.to_fs(:epoch))
+    payload = ActiveSupport::JSON.encode(roomId: room.id, at: created_at.to_f)
 
     room.memberships.unread.or(room.memberships.connected).pluck(:user_id).each do |user_id|
       ActionCable.server.broadcast UnreadRoomsChannel.stream_name_for(user_id), payload, coder: nil
diff --git a/lib/web_push/connections.rb b/lib/web_push/connections.rb
index df783fe..f151701 100644
--- a/lib/web_push/connections.rb
+++ b/lib/web_push/connections.rb
@@ -26,8 +26,9 @@ class WebPush::Connections
       end
   end
 
-  def initialize(keep_alive_timeout: 30)
+  def initialize(keep_alive_timeout: 30, max_idle: 150)
     @keep_alive_timeout = keep_alive_timeout
+    @max_idle = max_idle
     @idle = Hash.new { |idle, address| idle[address] = [] }
     @mutex = Mutex.new
     @pid = Process.pid
@@ -85,7 +86,7 @@ class WebPush::Connections
     def checkin(address, http)
       @mutex.synchronize do
         close_expired
-        if @shut_down
+        if @shut_down || @idle.values.sum(&:size) >= @max_idle
           close(http)
         else
           @idle[address].push [ http, now ]
diff --git a/test/channels/presence_channel_test.rb b/test/channels/presence_channel_test.rb
index 881f255..719d26b 100644
--- a/test/channels/presence_channel_test.rb
+++ b/test/channels/presence_channel_test.rb
@@ -44,7 +44,7 @@ class PresenceChannelTest < ActionCable::Channel::TestCase
     membership = users(:david).memberships.first
 
     freeze_time do
-      assert_broadcast_on "user_#{users(:david).id}_reads", { room_id: membership.room_id, at: Time.current.to_fs(:epoch) } do
+      assert_broadcast_on "user_#{users(:david).id}_reads", { room_id: membership.room_id, at: Time.current.to_f } do
         subscribe room_id: membership.room_id
       end
     end
diff --git a/test/channels/unread_rooms_channel_test.rb b/test/channels/unread_rooms_channel_test.rb
index 079234b..e8be2f7 100644
--- a/test/channels/unread_rooms_channel_test.rb
+++ b/test/channels/unread_rooms_channel_test.rb
@@ -35,7 +35,7 @@ class UnreadRoomsChannelTest < ActionCable::Channel::TestCase
       end
     end
 
-    assert_equal [ { "roomId" => direct.id, "at" => message.created_at.to_fs(:epoch) } ], broadcasts
+    assert_equal [ { "roomId" => direct.id, "at" => message.created_at.to_f } ], broadcasts
   end
 
   private
diff --git a/test/lib/web_push/connections_test.rb b/test/lib/web_push/connections_test.rb
index d465702..b93ced3 100644
--- a/test/lib/web_push/connections_test.rb
+++ b/test/lib/web_push/connections_test.rb
@@ -135,6 +135,24 @@ class WebPush::ConnectionsTest < ActiveSupport::TestCase
     end
   end
 
+  test "the idle pool closes connections beyond its bound" do
+    connections = WebPush::Connections.new(max_idle: 1)
+
+    with_push_service do |server|
+      other = Server.new
+      connections.request(pinned_connection(server), push_request)
+      connections.request(pinned_connection(other), push_request)
+      assert other.hung_up?
+      assert_not server.hung_up?(within: 0.1)
+
+      connections.request(pinned_connection(server), push_request)
+      assert_equal 1, server.connections
+    ensure
+      connections.shutdown
+      other&.stop
+    end
+  end
+
   test "idle connections are closed after the keep-alive timeout and on shutdown" do
     connections = WebPush::Connections.new(keep_alive_timeout: 0)
 
diff --git a/test/system/unread_rooms_test.rb b/test/system/unread_rooms_test.rb
index f2164c4..d4b170a 100644
--- a/test/system/unread_rooms_test.rb
+++ b/test/system/unread_rooms_test.rb
@@ -55,8 +55,23 @@ class UnreadRoomsTest < ApplicationSystemTestCase
     end
   end
 
+  test "a message after a read in the same second marks the room unread" do
+    room = rooms(:designers)
+    user = users(:jz)
+    join_room rooms(:hq)
+    read_at = Time.current.change(usec: 100_000)
+
+    broadcast_unread_notice room, to: user, at: read_at - 1
+    assert_room_unread room
+    ActionCable.server.broadcast "user_#{user.id}_reads", { room_id: room.id, at: read_at.to_f }
+    assert_room_read room
+
+    broadcast_unread_notice room, to: user, at: read_at + 0.2
+    assert_room_unread room
+  end
+
   private
     def broadcast_unread_notice(room, to:, at:)
-      ActionCable.server.broadcast UnreadRoomsChannel.stream_name_for(to.id), { roomId: room.id, at: at.to_fs(:epoch) }
+      ActionCable.server.broadcast UnreadRoomsChannel.stream_name_for(to.id), { roomId: room.id, at: at.to_f }
     end
 end