diff --git a/d2m/actions/register-user.js b/d2m/actions/register-user.js
index a5fd0ef..508dd39 100644
--- a/d2m/actions/register-user.js
+++ b/d2m/actions/register-user.js
@@ -24,10 +24,18 @@ async function createSim(user) {
 	const mxid = "@" + localpart + ":cadence.moe"
 
 	// Save chosen name in the database forever
+	// Making this database change right away so that in a concurrent registration, the 2nd registration will already have generated a different localpart because it can see this row when it generates
 	db.prepare("INSERT INTO sim (discord_id, sim_name, localpart, mxid) VALUES (?, ?, ?, ?)").run(user.id, simName, localpart, mxid)
 
 	// Register matrix user with that name
-	await api.register(localpart)
+	try {
+		await api.register(localpart)
+	} catch (e) {
+		// If user creation fails, manually undo the database change. Still isn't perfect, but should help.
+		// (A transaction would be preferable, but I don't think it's safe to leave transaction open across event loop ticks.)
+		db.prepare("DELETE FROM sim WHERE discord_id = ?").run(user.id)
+		throw e
+	}
 	return mxid
 }
 
diff --git a/d2m/actions/send-message.js b/d2m/actions/send-message.js
index 630cf48..f828134 100644
--- a/d2m/actions/send-message.js
+++ b/d2m/actions/send-message.js
@@ -28,4 +28,4 @@ async function sendMessage(message) {
 	return eventID
 }
 
-module.exports.sendMessage = sendMessage
+module.exports.sendMessage = sendMessage
\ No newline at end of file
diff --git a/d2m/converters/user-to-mxid.js b/d2m/converters/user-to-mxid.js
index 35d9368..89e47a4 100644
--- a/d2m/converters/user-to-mxid.js
+++ b/d2m/converters/user-to-mxid.js
@@ -44,6 +44,7 @@ function* generateLocalpartAlternatives(preferences) {
 
 /**
  * Whole process for checking the database and generating the right sim name.
+ * It is very important this is not an async function: once the name has been chosen, the calling function should be able to immediately claim that name into the database in the same event loop tick.
  * @param {import("discord-api-types/v10").APIUser} user
  * @returns {string}
  */
diff --git a/d2m/converters/user-to-mxid.test.js b/d2m/converters/user-to-mxid.test.js
index 4c721fc..8c4c430 100644
--- a/d2m/converters/user-to-mxid.test.js
+++ b/d2m/converters/user-to-mxid.test.js
@@ -31,3 +31,7 @@ test("user2name: adds number suffix if name is unavailable (new username format)
 test("user2name: uses ID if name becomes too short", t => {
    t.equal(userToSimName({username: "f***", discriminator: "0001", id: "9"}), "9")
 })
+
+test("user2name: uses ID when name has only disallowed characters", t => {
+   t.equal(userToSimName({username: "!@#$%^&*", discriminator: "0001", id: "9"}), "9")
+})
\ No newline at end of file
diff --git a/d2m/discord-packets.js b/d2m/discord-packets.js
index 0d16cdc..3786393 100644
--- a/d2m/discord-packets.js
+++ b/d2m/discord-packets.js
@@ -6,15 +6,16 @@ const DiscordTypes = require("discord-api-types/v10")
 const passthrough = require("../passthrough")
 const { sync } = passthrough
 
-/** @type {typeof import("./event-dispatcher")} */
-const eventDispatcher = sync.require("./event-dispatcher")
-
 const utils = {
 	/**
 	 * @param {import("./discord-client")} client
 	 * @param {import("cloudstorm").IGatewayMessage} message
 	 */
 	onPacket(client, message) {
+		// requiring this later so that the client is already constructed by the time event-dispatcher is loaded
+		/** @type {typeof import("./event-dispatcher")} */
+		const eventDispatcher = sync.require("./event-dispatcher")
+
 		if (message.t === "READY") {
 			if (client.ready) return
 			client.ready = true
diff --git a/d2m/event-dispatcher.js b/d2m/event-dispatcher.js
index 8539044..83a1a70 100644
--- a/d2m/event-dispatcher.js
+++ b/d2m/event-dispatcher.js
@@ -2,9 +2,6 @@
 
 const {sync} = require("../passthrough")
 
-/** @type {import("./actions/create-space")}) */
-const createSpace = sync.require("./actions/create-space")
-
 /** @type {import("./actions/send-message")}) */
 const sendMessage = sync.require("./actions/send-message")
 
diff --git a/matrix/api.js b/matrix/api.js
index 04b7cd1..dbc39bc 100644
--- a/matrix/api.js
+++ b/matrix/api.js
@@ -28,6 +28,7 @@ function path(p, mxid) {
  * @returns {Promise<import("../types").R.Registered>}
  */
 function register(username) {
+   console.log(`[api] register: ${username}`)
    return mreq.mreq("POST", "/client/v3/register", {
       type: "m.login.application_service",
       username
@@ -38,6 +39,7 @@ function register(username) {
  * @returns {Promise<string>} room ID
  */
 async function createRoom(content) {
+   console.log(`[api] create room:`, content)
    /** @type {import("../types").R.RoomCreated} */
    const root = await mreq.mreq("POST", "/client/v3/createRoom", content)
    return root.room_id
@@ -74,6 +76,7 @@ function getAllState(roomID) {
  * @returns {Promise<string>} event ID
  */
 async function sendState(roomID, type, stateKey, content, mxid) {
+   console.log(`[api] state: ${roomID}: ${type}/${stateKey}`)
    assert.ok(type)
    assert.ok(stateKey)
    /** @type {import("../types").R.EventSent} */
@@ -82,6 +85,7 @@ async function sendState(roomID, type, stateKey, content, mxid) {
 }
 
 async function sendEvent(roomID, type, content, mxid) {
+   console.log(`[api] event to ${roomID} as ${mxid || "default sim"}`)
    /** @type {import("../types").R.EventSent} */
    const root = await mreq.mreq("PUT", path(`/client/v3/rooms/${roomID}/send/${type}/${makeTxnId.makeTxnId()}`, mxid), content)
    return root.event_id
diff --git a/matrix/mreq.js b/matrix/mreq.js
index 6c4eaa3..df34d91 100644
--- a/matrix/mreq.js
+++ b/matrix/mreq.js
@@ -11,11 +11,12 @@ const reg = sync.require("./read-registration.js")
 const baseUrl = "https://matrix.cadence.moe/_matrix"
 
 class MatrixServerError extends Error {
-	constructor(data) {
+	constructor(data, opts) {
 		super(data.error || data.errcode)
 		this.data = data
 		/** @type {string} */
 		this.errcode = data.errcode
+		this.opts = opts
 	}
 }
 
@@ -38,7 +39,7 @@ async function mreq(method, url, body, extra = {}) {
 	const res = await fetch(baseUrl + url, opts)
 	const root = await res.json()
 
-	if (!res.ok || root.errcode) throw new MatrixServerError(root)
+	if (!res.ok || root.errcode) throw new MatrixServerError(root, opts)
 	return root
 }
 
diff --git a/matrix/read-registration.test.js b/matrix/read-registration.test.js
new file mode 100644
index 0000000..9c7f828
--- /dev/null
+++ b/matrix/read-registration.test.js
@@ -0,0 +1,11 @@
+const {test} = require("supertape")
+const assert = require("assert")
+const reg = require("./read-registration")
+
+test("reg: has necessary parameters", t => {
+   const propertiesToCheck = ["sender_localpart", "id", "as_token", "namespace_prefix"]
+   t.deepEqual(
+      propertiesToCheck.filter(p => p in reg),
+      propertiesToCheck
+   )
+})
\ No newline at end of file
diff --git a/test/test.js b/test/test.js
index 1068136..4e01708 100644
--- a/test/test.js
+++ b/test/test.js
@@ -12,6 +12,7 @@ const sync = new HeatSync({watchFS: false})
 
 Object.assign(passthrough, { config, sync, db })
 
+require("../matrix/read-registration.test")
 require("../d2m/actions/create-room.test")
 require("../d2m/converters/user-to-mxid.test")
 require("../matrix/api.test")