diff --git a/packages/browser/src/client/orchestrator.ts b/packages/browser/src/client/orchestrator.ts
index 29cba9927..75ecd6a8c 100644
--- a/packages/browser/src/client/orchestrator.ts
+++ b/packages/browser/src/client/orchestrator.ts
@@ -353,7 +353,7 @@ export class IframeOrchestrator {
 
   private createTestIframe(iframeId: string) {
     const iframe = document.createElement('iframe')
-    const src = `/?sessionId=${getBrowserState().sessionId}&iframeId=${iframeId}`
+    const src = `/?sessionId=${getBrowserState().sessionId}&iframeId=${encodeURIComponent(iframeId)}`
     const config = getConfig()
 
     iframe.setAttribute('loading', 'eager')
diff --git a/test/browser/fixtures/file-path-encoding/a+b.test.ts b/test/browser/fixtures/file-path-encoding/a+b.test.ts
new file mode 100644
index 000000000..ce0531a15
--- /dev/null
+++ b/test/browser/fixtures/file-path-encoding/a+b.test.ts
@@ -0,0 +1,5 @@
+import { expect, test } from 'vitest'
+
+test('runs a test from a file whose path contains a plus sign', () => {
+  expect(true).toBe(true)
+})
diff --git a/test/browser/fixtures/file-path-encoding/vitest.config.ts b/test/browser/fixtures/file-path-encoding/vitest.config.ts
new file mode 100644
index 000000000..d5b967f26
--- /dev/null
+++ b/test/browser/fixtures/file-path-encoding/vitest.config.ts
@@ -0,0 +1,10 @@
+import { defineConfig } from 'vitest/config'
+
+export default defineConfig({
+  test: {
+    browser: {
+      enabled: true,
+      headless: true,
+    },
+  },
+})
diff --git a/test/browser/specs/file-path-encoding.test.ts b/test/browser/specs/file-path-encoding.test.ts
new file mode 100644
index 000000000..299b935a1
--- /dev/null
+++ b/test/browser/specs/file-path-encoding.test.ts
@@ -0,0 +1,20 @@
+import { expect, test } from 'vitest'
+import { instances, provider, runBrowserTests } from './utils'
+
+test('runs tests from files whose path contains a plus sign', async () => {
+  const { stderr, stdout, exitCode } = await runBrowserTests({
+    root: './fixtures/file-path-encoding',
+    reporters: ['verbose'],
+    browser: {
+      provider,
+      instances,
+    },
+  })
+
+  expect(stderr).toBe('')
+  expect(exitCode).toBe(0)
+
+  instances.forEach(({ browser }) => {
+    expect(stdout).toReportPassedTest('a+b.test.ts', browser)
+  })
+})