diff --git a/cypress/e2e/crypto/crypto.spec.ts b/cypress/e2e/crypto/crypto.spec.ts
index 2a55c21b05..b5db3871b8 100644
--- a/cypress/e2e/crypto/crypto.spec.ts
+++ b/cypress/e2e/crypto/crypto.spec.ts
@@ -158,8 +158,8 @@ describe("Cryptography", function () {
         cy.startSynapse("default")
             .as("synapse")
             .then((synapse: SynapseInstance) => {
-                cy.initTestUser(synapse, "Alice");
-                cy.getBot(synapse, { displayName: "Bob", autoAcceptInvites: false }).as("bob");
+                cy.initTestUser(synapse, "Alice", undefined, "alice_");
+                cy.getBot(synapse, { displayName: "Bob", autoAcceptInvites: false, userIdPrefix: "bob_" }).as("bob");
             });
     });
 
diff --git a/cypress/support/bot.ts b/cypress/support/bot.ts
index f4476af12f..78c83c5c8e 100644
--- a/cypress/support/bot.ts
+++ b/cypress/support/bot.ts
@@ -22,6 +22,10 @@ import { Credentials } from "./synapse";
 import Chainable = Cypress.Chainable;
 
 interface CreateBotOpts {
+    /**
+     * A prefix to use for the userid. If unspecified, "bot_" will be used.
+     */
+    userIdPrefix?: string;
     /**
      * Whether the bot should automatically accept all invites.
      */
@@ -41,6 +45,7 @@ interface CreateBotOpts {
 }
 
 const defaultCreateBotOptions = {
+    userIdPrefix: "bot_",
     autoAcceptInvites: true,
     startClient: true,
     bootstrapCrossSigning: true,
@@ -153,7 +158,7 @@ function setupBotClient(
 
 Cypress.Commands.add("getBot", (synapse: SynapseInstance, opts: CreateBotOpts): Chainable<MatrixClient> => {
     opts = Object.assign({}, defaultCreateBotOptions, opts);
-    const username = Cypress._.uniqueId("userId_");
+    const username = Cypress._.uniqueId(opts.userIdPrefix);
     const password = Cypress._.uniqueId("password_");
     return cy.registerUser(synapse, username, password, opts.displayName).then((credentials) => {
         cy.log(`Registered bot user ${username} with displayname ${opts.displayName}`);
diff --git a/cypress/support/login.ts b/cypress/support/login.ts
index 73300f7905..338da2f9db 100644
--- a/cypress/support/login.ts
+++ b/cypress/support/login.ts
@@ -37,11 +37,14 @@ declare global {
              * @param synapse the synapse returned by startSynapse
              * @param displayName the displayName to give the test user
              * @param prelaunchFn optional function to run before the app is visited
+             * @param userIdPrefix optional prefix to use for the generated user id. If unspecified, `user_` will be
+             *     useed.
              */
             initTestUser(
                 synapse: SynapseInstance,
                 displayName: string,
                 prelaunchFn?: () => void,
+                userIdPrefix?: string,
             ): Chainable<UserCredentials>;
             /**
              * Logs into synapse with the given username/password
@@ -91,7 +94,12 @@ Cypress.Commands.add(
 // eslint-disable-next-line max-len
 Cypress.Commands.add(
     "initTestUser",
-    (synapse: SynapseInstance, displayName: string, prelaunchFn?: () => void): Chainable<UserCredentials> => {
+    (
+        synapse: SynapseInstance,
+        displayName: string,
+        prelaunchFn?: () => void,
+        userIdPrefix = "user_",
+    ): Chainable<UserCredentials> => {
         // XXX: work around Cypress not clearing IDB between tests
         cy.window({ log: false }).then((win) => {
             win.indexedDB.databases()?.then((databases) => {
@@ -101,7 +109,7 @@ Cypress.Commands.add(
             });
         });
 
-        const username = Cypress._.uniqueId("userId_");
+        const username = Cypress._.uniqueId(userIdPrefix);
         const password = Cypress._.uniqueId("password_");
         return cy
             .registerUser(synapse, username, password, displayName)