diff --git a/spec/integ/matrix-client-methods.spec.ts b/spec/integ/matrix-client-methods.spec.ts
index 5508ceaf031..f2ff9e6df77 100644
--- a/spec/integ/matrix-client-methods.spec.ts
+++ b/spec/integ/matrix-client-methods.spec.ts
@@ -1337,27 +1337,38 @@ describe("MatrixClient", function() {
         });
     });
 
-    describe("registerWithIdentityServer", () => {
-        it("should pass data to POST request", async () => {
-            const token = {
-                access_token: "access_token",
-                token_type: "Bearer",
-                matrix_server_name: "server_name",
-                expires_in: 12345,
-            };
+    describe("setPowerLevel", () => {
+        it.each([
+            {
+                userId: "alice@localhost",
+                expectation: {
+                    "alice@localhost": 100,
+                },
+            },
+            {
+                userId: ["alice@localhost", "bob@localhost"],
+                expectation: {
+                    "alice@localhost": 100,
+                    "bob@localhost": 100,
+                },
+            },
+        ])("should modify power levels of $userId correctly", async ({ userId, expectation }) => {
+            const event = {
+                getType: () => "m.room.power_levels",
+                getContent: () => ({
+                    users: {
+                        "alice@localhost": 50,
+                    },
+                }),
+            } as MatrixEvent;
 
-            httpBackend!.when("POST", "/account/register").check(req => {
-                expect(req.data).toStrictEqual(token);
-            }).respond(200, {
-                access_token: "at",
-                token: "tt",
-            });
+            httpBackend!.when("PUT", "/state/m.room.power_levels").check(req => {
+                expect(req.data.users).toStrictEqual(expectation);
+            }).respond(200, {});
 
-            const prom = client!.registerWithIdentityServer(token);
+            const prom = client!.setPowerLevel("!room_id:server", userId, 100, event);
             await httpBackend!.flushAllExpected();
-            const resp = await prom;
-            expect(resp.access_token).toBe("at");
-            expect(resp.token).toBe("tt");
+            await prom;
         });
     });
 });
diff --git a/src/client.ts b/src/client.ts
index b091a31ec45..d8bb110630f 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -3795,9 +3795,9 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
     }
 
     /**
-     * Set a user's power level.
+     * Set a power level to one or multiple users.
      * @param {string} roomId
-     * @param {string} userId
+     * @param {string|string[]} userId
      * @param {Number} powerLevel
      * @param {MatrixEvent} event
      * @return {Promise} Resolves: to an ISendEventResponse object
@@ -3805,19 +3805,25 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      */
     public setPowerLevel(
         roomId: string,
-        userId: string,
+        userId: string | string[],
         powerLevel: number,
         event: MatrixEvent,
     ): Promise<ISendEventResponse> {
         let content = {
-            users: {},
+            users: {} as Record<string, number>,
         };
-        if (event?.getType() === EventType.RoomPowerLevels) {
+        if (event.getType() === EventType.RoomPowerLevels) {
             // take a copy of the content to ensure we don't corrupt
             // existing client state with a failed power level change
             content = utils.deepCopy(event.getContent());
         }
-        content.users[userId] = powerLevel;
+        if (Array.isArray(userId)) {
+            for (const user of userId) {
+                content.users[user] = powerLevel;
+            }
+        } else {
+            content.users[userId] = powerLevel;
+        }
         const path = utils.encodeUri("/rooms/$roomId/state/m.room.power_levels", {
             $roomId: roomId,
         });