diff --git a/packages/opencode/src/bus/bus-event.ts b/packages/opencode/src/bus/bus-event.ts
index bb9b3f497f..90a0668dba 100644
--- a/packages/opencode/src/bus/bus-event.ts
+++ b/packages/opencode/src/bus/bus-event.ts
@@ -23,16 +23,12 @@ export function define<Type extends string, P extends ZodType>(
   properties: P,
 ): { type: Type; properties: P }
 export function define(type: string, properties: unknown) {
-  const zodProperties = isEffectSchema(properties) ? zod(properties) : (properties as ZodType)
+  const zodProperties = Schema.isSchema(properties) ? zod(properties) : (properties as ZodType)
   const result = { type, properties: zodProperties }
   registry.set(type, result as Definition)
   return result
 }
 
-function isEffectSchema(value: unknown): value is Schema.Top {
-  return typeof value === "object" && value !== null && "ast" in value
-}
-
 export function payloads() {
   return registry
     .entries()
diff --git a/packages/opencode/src/sync/index.ts b/packages/opencode/src/sync/index.ts
index 6fdad16621..fdedff0366 100644
--- a/packages/opencode/src/sync/index.ts
+++ b/packages/opencode/src/sync/index.ts
@@ -117,7 +117,7 @@ export function define<
 }
 
 function toZodObject(value: ZodObject | Schema.Top): z.ZodObject {
-  if (typeof value === "object" && value !== null && "ast" in value) {
+  if (Schema.isSchema(value)) {
     return zod(value as Schema.Top) as unknown as z.ZodObject
   }
   return value as z.ZodObject
diff --git a/packages/opencode/test/bus/bus.test.ts b/packages/opencode/test/bus/bus.test.ts
index 3df179787d..7cde38a014 100644
--- a/packages/opencode/test/bus/bus.test.ts
+++ b/packages/opencode/test/bus/bus.test.ts
@@ -1,4 +1,5 @@
 import { afterEach, describe, expect, test } from "bun:test"
+import { Schema } from "effect"
 import z from "zod"
 import { Bus } from "../../src/bus"
 import { BusEvent } from "../../src/bus/bus-event"
@@ -10,6 +11,8 @@ const TestEvent = {
   Pong: BusEvent.define("test.pong", z.object({ message: z.string() })),
 }
 
+const EffectTestEvent = BusEvent.define("test.effect-schema.ping", Schema.Struct({ value: Schema.Number }))
+
 function withInstance(directory: string, fn: () => Promise<void>) {
   return Instance.provide({ directory, fn })
 }
@@ -76,6 +79,22 @@ describe("Bus", () => {
         await Bus.publish(TestEvent.Ping, { value: 1 })
       })
     })
+
+    test("accepts Effect Schema event definitions", async () => {
+      await using tmp = await tmpdir()
+      const received: number[] = []
+
+      await withInstance(tmp.path, async () => {
+        Bus.subscribe(EffectTestEvent, (evt) => {
+          received.push(evt.properties.value)
+        })
+        await Bun.sleep(10)
+        await Bus.publish(EffectTestEvent, { value: 42 })
+        await Bun.sleep(10)
+      })
+
+      expect(received).toEqual([42])
+    })
   })
 
   describe("unsubscribe", () => {
diff --git a/packages/opencode/test/sync/index.test.ts b/packages/opencode/test/sync/index.test.ts
index 866bcaa31a..81c78132ec 100644
--- a/packages/opencode/test/sync/index.test.ts
+++ b/packages/opencode/test/sync/index.test.ts
@@ -1,4 +1,5 @@
 import { describe, test, expect, beforeEach, afterEach, afterAll } from "bun:test"
+import { Schema } from "effect"
 import { tmpdir } from "../fixture/fixture"
 import z from "zod"
 import { Bus } from "../../src/bus"
@@ -128,6 +129,51 @@ describe("SyncEvent", () => {
         })
       }),
     )
+
+    test(
+      "accepts Effect Schema event definitions",
+      withInstance(async () => {
+        SyncEvent.reset()
+        try {
+          const Created = SyncEvent.define({
+            type: "item.effect.created",
+            version: 1,
+            aggregate: "id",
+            schema: Schema.Struct({ id: Schema.String, name: Schema.String }),
+          })
+
+          SyncEvent.init({
+            projectors: [SyncEvent.project(Created, () => {})],
+          })
+
+          const events: Array<{
+            type: string
+            properties: { id: string; name: string }
+          }> = []
+          const received = new Promise<void>((resolve) => {
+            Bus.subscribeAll((event) => {
+              events.push(event)
+              resolve()
+            })
+          })
+
+          SyncEvent.run(Created, { id: "evt_1", name: "schema" })
+
+          await received
+          expect(events).toEqual([
+            {
+              type: "item.effect.created",
+              properties: {
+                id: "evt_1",
+                name: "schema",
+              },
+            },
+          ])
+        } finally {
+          setup()
+        }
+      }),
+    )
   })
 
   describe("replay", () => {