diff --git a/packages/wdio-browserstack-service/src/@types/bstack-service-types.d.ts b/packages/wdio-browserstack-service/src/@types/bstack-service-types.d.ts
deleted file mode 100644
index ff43c67d27a..00000000000
--- a/packages/wdio-browserstack-service/src/@types/bstack-service-types.d.ts
+++ /dev/null
@@ -1,17 +0,0 @@
-declare namespace WebdriverIO {
-    interface Browser {
-        getAccessibilityResultsSummary: () => Promise<Record<string, unknown>>,
-        getAccessibilityResults: () => Promise<Array<Record<string, unknown>>>,
-        performScan: () => Promise<Record<string, unknown> | undefined>,
-        startA11yScanning: () => Promise<void>,
-        stopA11yScanning: () => Promise<void>
-    }
-
-    interface MultiRemoteBrowser {
-        getAccessibilityResultsSummary: () => Promise<Record<string, unknown>>,
-        getAccessibilityResults: () => Promise<Array<Record<string, unknown>>>,
-        performScan: () => Promise<Record<string, unknown> | undefined>,
-        startA11yScanning: () => Promise<void>,
-        stopA11yScanning: () => Promise<void>
-    }
-}
diff --git a/packages/wdio-browserstack-service/src/accessibility-handler.ts b/packages/wdio-browserstack-service/src/accessibility-handler.ts
index 76ae8329cc0..ff1ef903935 100644
--- a/packages/wdio-browserstack-service/src/accessibility-handler.ts
+++ b/packages/wdio-browserstack-service/src/accessibility-handler.ts
@@ -1,4 +1,3 @@
-/// <reference path="./@types/bstack-service-types.d.ts" />
 import util from 'node:util'
 
 import type { Capabilities, Frameworks, Options } from '@wdio/types'
diff --git a/packages/wdio-browserstack-service/src/cli/modules/accessibilityModule.ts b/packages/wdio-browserstack-service/src/cli/modules/accessibilityModule.ts
index d71be0fe25c..1ad0d37159e 100644
--- a/packages/wdio-browserstack-service/src/cli/modules/accessibilityModule.ts
+++ b/packages/wdio-browserstack-service/src/cli/modules/accessibilityModule.ts
@@ -1,4 +1,3 @@
-/// <reference path="../../@types/bstack-service-types.d.ts" />
 import BaseModule from './baseModule.js'
 import { BrowserstackCLI } from '../index.js'
 import { BStackLogger } from '../cliLogger.js'
diff --git a/packages/wdio-browserstack-service/src/index.ts b/packages/wdio-browserstack-service/src/index.ts
index 32b65e41f1a..1c9ca3e1fef 100644
--- a/packages/wdio-browserstack-service/src/index.ts
+++ b/packages/wdio-browserstack-service/src/index.ts
@@ -20,6 +20,14 @@ export * from './types.js'
 declare global {
     namespace WebdriverIO {
         interface ServiceOption extends BrowserstackConfig {}
+
+        interface Browser {
+            getAccessibilityResultsSummary: () => Promise<Record<string, unknown>>,
+            getAccessibilityResults: () => Promise<Array<Record<string, unknown>>>,
+            performScan: () => Promise<Record<string, unknown> | undefined>,
+            startA11yScanning: () => Promise<void>,
+            stopA11yScanning: () => Promise<void>
+        }
     }
     interface State {
         value: number,
diff --git a/tests/typings/webdriverio/browserstackService.ts b/tests/typings/webdriverio/browserstackService.ts
new file mode 100644
index 00000000000..2657f017ac0
--- /dev/null
+++ b/tests/typings/webdriverio/browserstackService.ts
@@ -0,0 +1,30 @@
+import { expectType } from 'tsd'
+import { browser } from '@wdio/globals'
+
+/**
+ * Regression guard for the @wdio/browserstack-service accessibility
+ * augmentation of WebdriverIO.Browser.
+ *
+ * These five methods are declared inside
+ *   declare global { namespace WebdriverIO { interface Browser { ... } } }
+ * in packages/wdio-browserstack-service/src/index.ts. They previously lived
+ * in an un-emitted ambient .d.ts file and silently never reached the published
+ * build/index.d.ts, so consumers lost the typings. This file pulls in the
+ * published @wdio/browserstack-service types (it is listed in this suite's
+ * tsconfig.json `types` array) and fails `test:typings:webdriverio` if any of
+ * the five methods ever stops being typed on WebdriverIO.Browser again.
+ */
+;(async () => {
+    expectType<() => Promise<Record<string, unknown>>>(browser.getAccessibilityResultsSummary)
+    expectType<() => Promise<Array<Record<string, unknown>>>>(browser.getAccessibilityResults)
+    expectType<() => Promise<Record<string, unknown> | undefined>>(browser.performScan)
+    expectType<() => Promise<void>>(browser.startA11yScanning)
+    expectType<() => Promise<void>>(browser.stopA11yScanning)
+
+    // also assert the call-site return types resolve as declared
+    expectType<Record<string, unknown>>(await browser.getAccessibilityResultsSummary())
+    expectType<Array<Record<string, unknown>>>(await browser.getAccessibilityResults())
+    expectType<Record<string, unknown> | undefined>(await browser.performScan())
+    expectType<void>(await browser.startA11yScanning())
+    expectType<void>(await browser.stopA11yScanning())
+})