diff --git a/src/interactive-auth.js b/src/interactive-auth.js
index 200c5be58..90b17fc0d 100644
--- a/src/interactive-auth.js
+++ b/src/interactive-auth.js
@@ -55,6 +55,12 @@ const MSISDN_STAGE_TYPE = "m.login.msisdn";
  *     promise which resolves to the successful response or rejects with a
  *     MatrixError.
  *
+ * @param {function(bool): module:client.Promise} opts.setBusy
+ *     called whenever the interactive auth logic is busy submitting
+ *     information provided by the user. After this has been called with
+ *     true the UI should indicate that a request is in progress until it
+ *     is called again with false.
+ *
  * @param {function(string, object?)} opts.stateUpdated
  *     called when the status of the UI auth changes, ie. when the state of
  *     an auth stage changes of when the auth flow moves to a new stage.
@@ -101,6 +107,7 @@ function InteractiveAuth(opts) {
     this._matrixClient = opts.matrixClient;
     this._data = opts.authData || {};
     this._requestCallback = opts.doRequest;
+    this._setBusyCallback = opts.setBusy;
     // startAuthStage included for backwards compat
     this._stateUpdatedCallback = opts.stateUpdated || opts.startAuthStage;
     this._resolveFunc = null;
@@ -117,7 +124,9 @@ function InteractiveAuth(opts) {
     this._chosenFlow = null;
     this._currentStage = null;
 
-    this._polling = false;
+    // if we are currently trying to submit an auth dict (which includes polling)
+    // the promise the will resolve/reject when it completes
+    this._submitPromise = false;
 }
 
 InteractiveAuth.prototype = {
@@ -138,7 +147,10 @@ InteractiveAuth.prototype = {
             // if we have no flows, try a request (we'll have
             // just a session ID in _data if resuming)
             if (!this._data.flows) {
-                this._doRequest(this._data);
+                this._setBusyCallback(true);
+                this._doRequest(this._data).finally(() => {
+                    this._setBusyCallback(false);
+                });
             } else {
                 this._startNextAuthStage();
             }
@@ -152,7 +164,9 @@ InteractiveAuth.prototype = {
      */
     poll: async function() {
         if (!this._data.session) return;
-        if (this._polling) return;
+        // if we currently have a request in flight, there's no point making
+        // another just to check what the status is
+        if (this._submitPromise) return;
 
         let authDict = {};
         if (this._currentStage == EMAIL_STAGE_TYPE) {
@@ -173,12 +187,7 @@ InteractiveAuth.prototype = {
             }
         }
 
-        this._polling = true;
-        try {
-            await this.submitAuthDict(authDict, true);
-        } finally {
-            this._polling = false;
-        }
+        this.submitAuthDict(authDict, true);
     },
 
     /**
@@ -235,13 +244,37 @@ InteractiveAuth.prototype = {
             throw new Error("submitAuthDict() called before attemptAuth()");
         }
 
+        if (!background && this._setBusyCallback) {
+            this._setBusyCallback(true);
+        }
+
+        // if we're currently trying a request, wait for it to finish
+        // as otherwise we can get multiple 200 responses which can mean
+        // things like multiple logins for register requests.
+        // (but discard any expections as we only care when its done,
+        // not whether it worked or not)
+        while (this._submitPromise) {
+            try {
+                await this._submitPromise;
+            } catch (e) {
+            }
+        }
+
         // use the sessionid from the last request.
         const auth = {
             session: this._data.session,
         };
         utils.extend(auth, authData);
 
-        await this._doRequest(auth, background);
+        try {
+            // NB. the 'background' flag is deprecated by the setBusy
+            // callback and is here for backwards compat
+            this._submitPromise = this._doRequest(auth, background);
+            await this._submitPromise;
+        } finally {
+            this._submitPromise = null;
+            if (!background) this._setBusyCallback(false);
+        }
     },
 
     /**