diff --git a/src/extensions/sync.ts b/src/extensions/sync.ts
index 14079f26..651eaf40 100644
--- a/src/extensions/sync.ts
+++ b/src/extensions/sync.ts
@@ -40,7 +40,13 @@ export function sync(db: Database<any>) {
     'message',
     (event: MessageEvent<DatabaseMessageEventData<any>>) => {
       const { operationType, payload } = event.data
-      console.warn('[sync]', operationType, payload)
+      const [sourceId, ...args] = payload
+
+      // Ignore messages originating from unrelated databases.
+      // Useful in case of multiple databases on the same page.
+      if (db.id !== sourceId) {
+        return
+      }
 
       // Remove database event listener for the signaled operation
       // to prevent an infinite loop when applying this operation.
@@ -49,7 +55,7 @@ export function sync(db: Database<any>) {
       // Apply the database operation signaled from another client
       // to the current database instance.
       // @ts-ignore
-      db[operationType](...payload)
+      db[operationType](...args)
 
       // Re-attach database event listeners.
       restoreListeners()
diff --git a/test/extensions/sync.multiple.runtime.js b/test/extensions/sync.multiple.runtime.js
new file mode 100644
index 00000000..ddd96d4e
--- /dev/null
+++ b/test/extensions/sync.multiple.runtime.js
@@ -0,0 +1,15 @@
+import { factory, primaryKey } from '@mswjs/data'
+
+window.db = factory({
+  user: {
+    id: primaryKey(String),
+    firstName: String,
+  },
+})
+
+window.secondDb = factory({
+  user: {
+    id: primaryKey(String),
+    firstName: String,
+  },
+})
diff --git a/test/extensions/sync.test.ts b/test/extensions/sync.test.ts
index 581e98dc..c59f2355 100644
--- a/test/extensions/sync.test.ts
+++ b/test/extensions/sync.test.ts
@@ -2,8 +2,14 @@ import * as path from 'path'
 import { createBrowser, CreateBrowserApi, pageWith } from 'page-with'
 import { FactoryAPI } from '../../src/glossary'
 
+interface User {
+  id: string
+  firstName: string
+}
+
 declare namespace window {
-  export const db: FactoryAPI<any>
+  export const db: FactoryAPI<{ user: User }>
+  export const secondDb: FactoryAPI<{ user: User }>
 }
 
 let browser: CreateBrowserApi
@@ -41,10 +47,7 @@ test('synchornizes entity create across multiple clients', async () => {
     })
   })
 
-  const users = await secondPage.evaluate(() => {
-    return window.db.user.getAll()
-  })
-  expect(users).toEqual([
+  expect(await secondPage.evaluate(() => window.db.user.getAll())).toEqual([
     {
       __type: 'user',
       __primaryKey: 'id',
@@ -90,15 +93,12 @@ test('synchornizes entity update across multiple clients', async () => {
       firstName: 'Kate',
     },
   ]
-  const users = await secondPage.evaluate(() => {
-    return window.db.user.getAll()
-  })
-  expect(users).toEqual(expectedUsers)
-
-  const extraneousUsers = await runtime.page.evaluate(() => {
-    return window.db.user.getAll()
-  })
-  expect(extraneousUsers).toEqual(expectedUsers)
+  expect(await secondPage.evaluate(() => window.db.user.getAll())).toEqual(
+    expectedUsers,
+  )
+  expect(await runtime.page.evaluate(() => window.db.user.getAll())).toEqual(
+    expectedUsers,
+  )
 })
 
 test('synchronizes entity delete across multiple clients', async () => {
@@ -126,13 +126,92 @@ test('synchronizes entity delete across multiple clients', async () => {
     })
   })
 
-  const users = await secondPage.evaluate(() => {
-    return window.db.user.getAll()
+  expect(await secondPage.evaluate(() => window.db.user.getAll())).toEqual([])
+  expect(await runtime.page.evaluate(() => window.db.user.getAll())).toEqual([])
+})
+
+test('handles events from multiple database instances separately', async () => {
+  const runtime = await pageWith({
+    example: path.resolve(__dirname, 'sync.multiple.runtime.js'),
+  })
+  const secondPage = await runtime.context.newPage()
+  await secondPage.goto(runtime.origin)
+  await runtime.page.bringToFront()
+
+  const john = {
+    __type: 'user',
+    __primaryKey: 'id',
+    id: 'abc-123',
+    firstName: 'John',
+  }
+
+  const kate = {
+    __type: 'user',
+    __primaryKey: 'id',
+    id: 'def-456',
+    firstName: 'Kate',
+  }
+
+  // Create a new user in the first database.
+  await runtime.page.evaluate(() => {
+    window.db.user.create({ id: 'abc-123', firstName: 'John' })
+  })
+  expect(await runtime.page.evaluate(() => window.db.user.getAll())).toEqual([
+    john,
+  ])
+  expect(await secondPage.evaluate(() => window.db.user.getAll())).toEqual([
+    john,
+  ])
+
+  // No entities are created in the second, unrelated database.
+  expect(
+    await secondPage.evaluate(() => {
+      return window.secondDb.user.getAll()
+    }),
+  ).toEqual([])
+
+  await secondPage.evaluate(() => {
+    window.secondDb.user.create({ id: 'def-456', firstName: 'Kate' })
+  })
+
+  // A new entity created in a different database is synchronized in another client.
+  expect(
+    await runtime.page.evaluate(() => window.secondDb.user.getAll()),
+  ).toEqual([kate])
+
+  // An unrelated database does not contain a newly created entity.
+  expect(await runtime.page.evaluate(() => window.db.user.getAll())).toEqual([
+    john,
+  ])
+})
+
+test('handles events from multiple databases on different hostnames', async () => {
+  const firstRuntime = await pageWith({
+    example: path.resolve(__dirname, 'sync.runtime.js'),
+  })
+  const secondRuntime = await pageWith({
+    example: path.resolve(__dirname, 'sync.multiple.runtime.js'),
   })
-  expect(users).toEqual([])
+  expect(firstRuntime.origin).not.toEqual(secondRuntime.origin)
 
-  const extraneousUsers = await runtime.page.evaluate(() => {
-    return window.db.user.getAll()
+  await firstRuntime.page.evaluate(() => {
+    window.db.user.create({ id: 'abc-123', firstName: 'John' })
   })
-  expect(extraneousUsers).toEqual([])
+  expect(
+    await secondRuntime.page.evaluate(() => window.db.user.getAll()),
+  ).toEqual([])
+
+  await secondRuntime.page.evaluate(() => {
+    window.db.user.create({ id: 'def-456', firstName: 'Kate' })
+  })
+  expect(
+    await firstRuntime.page.evaluate(() => window.db.user.getAll()),
+  ).toEqual([
+    {
+      __type: 'user',
+      __primaryKey: 'id',
+      id: 'abc-123',
+      firstName: 'John',
+    },
+  ])
 })