diff --git a/packages/opencode/src/config/config.ts b/packages/opencode/src/config/config.ts
index 2527303d92b5..52521ebe791a 100644
--- a/packages/opencode/src/config/config.ts
+++ b/packages/opencode/src/config/config.ts
@@ -289,9 +289,9 @@ export const layer = Layer.effect(
       const hasIgnore = yield* fs.existsSafe(gitignore)
       if (!hasIgnore) {
         yield* fs
-          .writeFileString(
+          .writeWithDirs(
             gitignore,
-            ["node_modules", "package.json", "package-lock.json", "bun.lock", ".gitignore"].join("\n"),
+            Buffer.from(["node_modules", "package.json", "package-lock.json", "bun.lock", ".gitignore"].join("\n")),
           )
           .pipe(
             Effect.catchIf(
diff --git a/packages/opencode/test/config/config.test.ts b/packages/opencode/test/config/config.test.ts
index c016431bc781..624abfb1a5b5 100644
--- a/packages/opencode/test/config/config.test.ts
+++ b/packages/opencode/test/config/config.test.ts
@@ -919,6 +919,23 @@ it.effect("installs dependencies in writable OPENCODE_CONFIG_DIR", () =>
   }).pipe(Effect.provide(testInstanceStoreLayer), Effect.provide(CrossSpawnSpawner.defaultLayer)),
 )
 
+it.effect("creates .gitignore in OPENCODE_CONFIG_DIR when directory does not yet exist", () =>
+  Effect.gen(function* () {
+    const dir = yield* tmpdirScoped()
+    const configDir = path.join(dir, "nonexistent-config-dir")
+
+    yield* withProcessEnv(
+      "OPENCODE_CONFIG_DIR",
+      configDir,
+      Config.Service.use((svc) => svc.get().pipe(Effect.andThen(svc.waitForDependencies()))).pipe(
+        provideInstanceEffect(dir),
+      ),
+    )
+
+    expect(yield* FSUtil.use.readFileString(path.join(configDir, ".gitignore"))).toContain("node_modules")
+  }).pipe(Effect.provide(testInstanceStoreLayer), Effect.provide(CrossSpawnSpawner.defaultLayer)),
+)
+
 // Note: deduplication and serialization of npm installs is now handled by the
 // core Npm.Service (via EffectFlock). Those behaviors are tested in the core
 // package's npm tests, not here.