diff --git a/packages/opencode/src/config/config.ts b/packages/opencode/src/config/config.ts
index 86238f1a844c..3820c57b996d 100644
--- a/packages/opencode/src/config/config.ts
+++ b/packages/opencode/src/config/config.ts
@@ -230,7 +230,8 @@ const layer = Layer.effect(
       yield* Effect.promise(() => resolveLoadedPlugins(data, options.path))
       if (!data.$schema) {
         data.$schema = "https://opencode.ai/config.json"
-        const updated = text.replace(/^\s*\{/, '{\n  "$schema": "https://opencode.ai/config.json",')
+        const comma = Object.keys(parsed).length ? "," : ""
+        const updated = text.replace(/^\s*\{/, `{\n  "$schema": "https://opencode.ai/config.json"${comma}`)
         yield* fs.writeFileString(options.path, updated).pipe(Effect.catch(() => Effect.void))
       }
       return data
diff --git a/packages/opencode/test/config/config.test.ts b/packages/opencode/test/config/config.test.ts
index e281831ddfa8..4ac956e813d3 100644
--- a/packages/opencode/test/config/config.test.ts
+++ b/packages/opencode/test/config/config.test.ts
@@ -528,6 +528,19 @@ it.instance("preserves env variables when adding $schema to config", () =>
   ),
 )
 
+it.instance("adds $schema to an empty JSON config without a trailing comma", () =>
+  Effect.gen(function* () {
+    const test = yield* TestInstance
+    const file = path.join(test.directory, "opencode.json")
+    yield* FSUtil.use.writeWithDirs(file, "{}")
+
+    yield* Config.use.get()
+
+    const content = yield* FSUtil.use.readFileString(file)
+    expect(JSON.parse(content)).toEqual({ $schema: "https://opencode.ai/config.json" })
+  }),
+)
+
 it.instance("handles file inclusion substitution", () =>
   Effect.gen(function* () {
     const test = yield* TestInstance