diff --git a/.changeset/nasty-queens-pull.md b/.changeset/nasty-queens-pull.md
new file mode 100644
index 0000000000..59d3076901
--- /dev/null
+++ b/.changeset/nasty-queens-pull.md
@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+ensure all Data.Error arguments are preserved in .toJSON
diff --git a/packages/effect/src/Data.ts b/packages/effect/src/Data.ts
index ac4d27bd41..6b02cc2df7 100644
--- a/packages/effect/src/Data.ts
+++ b/packages/effect/src/Data.ts
@@ -530,13 +530,18 @@ export const Error: new<A extends Record<string, any> = {}>(
   args: Types.Equals<A, {}> extends true ? void
     : { readonly [P in keyof A]: A[P] }
 ) => Cause.YieldableError & Readonly<A> = (function() {
+  const plainArgsSymbol = Symbol.for("effect/Data/Error/plainArgs")
   return class Base extends core.YieldableError {
     constructor(args: any) {
       super(args?.message, args?.cause ? { cause: args.cause } : undefined)
       if (args) {
         Object.assign(this, args)
+        Object.defineProperty(this, plainArgsSymbol, { value: args, enumerable: false })
       }
     }
+    toJSON() {
+      return { ...(this as any)[plainArgsSymbol], ...this }
+    }
   } as any
 })()
 
diff --git a/packages/effect/test/Data.test.ts b/packages/effect/test/Data.test.ts
index 2420c6c1de..7fab66478e 100644
--- a/packages/effect/test/Data.test.ts
+++ b/packages/effect/test/Data.test.ts
@@ -279,5 +279,24 @@ describe("Data", () => {
       expect(e.message).toStrictEqual("Oh no!")
       expect(e.a).toStrictEqual(1)
     })
+
+    it("toJSON includes all args", () => {
+      class MyError extends Data.Error<{ message: string; a: number; cause: string }> {}
+      const e = new MyError({ message: "Oh no!", a: 1, cause: "Boom" })
+      assert.deepStrictEqual(e.toJSON(), { message: "Oh no!", a: 1, cause: "Boom" })
+    })
+  })
+
+  describe("TaggedError", () => {
+    it("toJSON includes all args", () => {
+      class MyError extends Data.TaggedError("MyError")<{ message: string; a: number; cause: string }> {}
+      const e = new MyError({ message: "Oh no!", a: 1, cause: "Boom" })
+      assert.deepStrictEqual(e.toJSON(), {
+        _tag: "MyError",
+        message: "Oh no!",
+        a: 1,
+        cause: "Boom"
+      })
+    })
   })
 })