diff --git a/config/default.yaml b/config/default.yaml
index c451cea..3caeb00 100644
--- a/config/default.yaml
+++ b/config/default.yaml
@@ -74,3 +74,11 @@ automaticallyRedactForReasons:
 # A list of rooms to protect (matrix.to URLs)
 protectedRooms:
   - "https://matrix.to/#/#yourroom:example.org"
+
+# Set this option to true to protect every room the bot is joined to. Note that
+# this effectively makes the protectedRooms and associated commands useless because
+# the bot by nature must be joined to the room to protect it.
+#
+# Note: the management room is *excluded* from this condition. Add it to the
+# protected rooms to protect it.
+protectAllJoinedRooms: false
diff --git a/package.json b/package.json
index 1a25ce8..68c6c65 100644
--- a/package.json
+++ b/package.json
@@ -27,6 +27,6 @@
     "config": "^3.2.2",
     "escape-html": "^1.0.3",
     "js-yaml": "^3.13.1",
-    "matrix-bot-sdk": "^0.4.0"
+    "matrix-bot-sdk": "^0.4.1"
   }
 }
diff --git a/src/Mjolnir.ts b/src/Mjolnir.ts
index 5cccc48..0273b39 100644
--- a/src/Mjolnir.ts
+++ b/src/Mjolnir.ts
@@ -44,6 +44,7 @@ export class Mjolnir {
     private protections: IProtection[] = [];
     private redactionQueue = new AutomaticRedactionQueue();
     private automaticRedactionReasons: MatrixGlob[] = [];
+    private protectedJoinedRoomIds: string[] = [];
 
     constructor(
         public readonly client: MatrixClient,
@@ -75,6 +76,15 @@ export class Mjolnir {
             }
         });
 
+        client.on("room.join", (roomId: string, event: any) => {
+            LogService.info("Mjolnir", `Joined ${roomId}`);
+            return this.resyncJoinedRooms();
+        });
+        client.on("room.leave", (roomId: string, event: any) => {
+            LogService.info("Mjolnir", `Left ${roomId}`);
+            return this.resyncJoinedRooms();
+        });
+
         client.getUserId().then(userId => {
             this.localpart = userId.split(':')[0].substring(1);
             return client.getUserProfile(userId);
@@ -115,6 +125,7 @@ export class Mjolnir {
         }).then(async () => {
             this.currentState = STATE_SYNCING;
             await logMessage(LogLevel.DEBUG, "Mjolnir@startup", "Loading protected rooms...");
+            await this.resyncJoinedRooms(false);
             try {
                  const data = await this.client.getAccountData(PROTECTED_ROOMS_EVENT_TYPE);
                  if (data && data['rooms']) {
@@ -138,8 +149,7 @@ export class Mjolnir {
     }
 
     public async addProtectedRoom(roomId: string) {
-        const permalink = Permalinks.forRoom(roomId);
-        this.protectedRooms[roomId] = permalink;
+        this.protectedRooms[roomId] = Permalinks.forRoom(roomId);
 
         let additionalProtectedRooms;
         try {
@@ -167,6 +177,23 @@ export class Mjolnir {
         await this.client.setAccountData(PROTECTED_ROOMS_EVENT_TYPE, additionalProtectedRooms);
     }
 
+    private async resyncJoinedRooms(withSync = true) {
+        if (!config.protectAllJoinedRooms) return;
+
+        const joinedRoomIds = (await this.client.getJoinedRooms()).filter(r => r !== config.managementRoom);
+        for (const roomId of this.protectedJoinedRoomIds) {
+            delete this.protectedRooms[roomId];
+        }
+        this.protectedJoinedRoomIds = joinedRoomIds;
+        for (const roomId of joinedRoomIds) {
+            this.protectedRooms[roomId] = Permalinks.forRoom(roomId);
+        }
+
+        if (withSync) {
+            await this.syncLists(config.verboseLogging);
+        }
+    }
+
     private async getEnabledProtections() {
         let enabled: string[] = [];
         try {
diff --git a/src/commands/ListProtectedRoomsCommand.ts b/src/commands/ListProtectedRoomsCommand.ts
index 007683a..c0f29fc 100644
--- a/src/commands/ListProtectedRoomsCommand.ts
+++ b/src/commands/ListProtectedRoomsCommand.ts
@@ -19,8 +19,8 @@ import { RichReply } from "matrix-bot-sdk";
 
 // !mjolnir rooms
 export async function execListProtectedRooms(roomId: string, event: any, mjolnir: Mjolnir) {
-    let html = "<b>Protected rooms:</b><br/><ul>";
-    let text = "Protected rooms:\n";
+    let html = `<b>Protected rooms (${Object.keys(mjolnir.protectedRooms).length}):</b><br/><ul>`;
+    let text = `Protected rooms (${Object.keys(mjolnir.protectedRooms).length}):\n`;
 
     let hasRooms = false;
     for (const roomId in mjolnir.protectedRooms) {
diff --git a/src/config.ts b/src/config.ts
index aaa5a5a..4697f97 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -37,6 +37,7 @@ interface IConfig {
     protectedRooms: string[]; // matrix.to urls
     fasterMembershipChecks: boolean;
     automaticallyRedactForReasons: string[]; // case-insensitive globs
+    protectAllJoinedRooms: boolean;
 
     /**
      * Config options only set at runtime. Try to avoid using the objects
diff --git a/yarn.lock b/yarn.lock
index d1b48c6..343f44f 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1534,10 +1534,10 @@ map-visit@^1.0.0:
   dependencies:
     object-visit "^1.0.0"
 
-matrix-bot-sdk@^0.4.0:
-  version "0.4.0"
-  resolved "https://registry.yarnpkg.com/matrix-bot-sdk/-/matrix-bot-sdk-0.4.0.tgz#a2189e9cdb01d34b2a9c56003167eb33b1a12752"
-  integrity sha512-ZIICFEYDsSX3emPnVRTV1FIV22zkt7KiJbTYN4rHQ3Z/rk66RB7Y+TMHxrkJCqPs3xVdaGmGkh5m+hNi4fibRg==
+matrix-bot-sdk@^0.4.1:
+  version "0.4.1"
+  resolved "https://registry.yarnpkg.com/matrix-bot-sdk/-/matrix-bot-sdk-0.4.1.tgz#4a0a5d5c20a8444612f760c689adba0e7dfe5424"
+  integrity sha512-ePsmL6ZOVLsSY06fqS3c/3ZWXtfoCk3vUcHyciU+tgRrJqPP2wV15vbs8gHdavIWXmwno3wK95Xc45oH6Uibhg==
   dependencies:
     "@types/express" "^4.17.2"
     bluebird "^3.7.1"