diff --git a/packages/opencode/src/mcp/browser.ts b/packages/opencode/src/mcp/browser.ts
index 73aecc846b..68f4f59b21 100644
--- a/packages/opencode/src/mcp/browser.ts
+++ b/packages/opencode/src/mcp/browser.ts
@@ -22,11 +22,14 @@ const layer = Layer.succeed(
           clearTimeout(timer)
           resume(Effect.fail(error))
         })
-        subprocess.on("exit", (code) => {
+        const onExit = (code: number | null) => {
           if (code === null || code === 0) return
           clearTimeout(timer)
           resume(Effect.fail(new Error(`Browser open failed with exit code ${code}`)))
-        })
+        }
+        subprocess.on("exit", onExit)
+        // On Windows and WSL, open() can return only after the launcher has exited.
+        onExit(subprocess.exitCode)
       })
     }),
   }),
diff --git a/packages/opencode/test/mcp/browser.test.ts b/packages/opencode/test/mcp/browser.test.ts
new file mode 100644
index 0000000000..81dea236ac
--- /dev/null
+++ b/packages/opencode/test/mcp/browser.test.ts
@@ -0,0 +1,36 @@
+import { expect, mock, test } from "bun:test"
+import { spawn } from "node:child_process"
+import { once } from "node:events"
+import { LayerNode } from "@opencode-ai/core/effect/layer-node"
+import { Effect } from "effect"
+
+await mock.module("@opencode-ai/core/open", () => ({
+  openUrl: async (url: string) => {
+    const code = new URL(url).pathname === "/successful" ? 0 : 23
+    const subprocess = spawn(process.execPath, ["-e", `process.exit(${code})`], { stdio: "ignore" })
+    await once(subprocess, "close")
+    return subprocess
+  },
+}))
+
+const { McpBrowser } = await import("../../src/mcp/browser")
+
+test("reports a browser launcher that exited before openUrl returned", async () => {
+  const error = await Effect.runPromise(
+    Effect.gen(function* () {
+      const browser = yield* McpBrowser.Service
+      return yield* Effect.flip(browser.open("https://example.com/authorize"))
+    }).pipe(Effect.provide(LayerNode.compile(McpBrowser.node))),
+  )
+
+  expect(error.message).toBe("Browser open failed with exit code 23")
+})
+
+test("accepts a browser launcher that exited successfully before openUrl returned", async () => {
+  await Effect.runPromise(
+    Effect.gen(function* () {
+      const browser = yield* McpBrowser.Service
+      yield* browser.open("https://example.com/successful")
+    }).pipe(Effect.provide(LayerNode.compile(McpBrowser.node))),
+  )
+})