diff --git a/src/js/bun/ffi.ts b/src/js/bun/ffi.ts
index 3c885ccf1368..b406273a7d89 100644
--- a/src/js/bun/ffi.ts
+++ b/src/js/bun/ffi.ts
@@ -69,7 +69,7 @@ var ffi = globalThis.Bun.FFI;
 const ptr = (arg1, arg2) => (typeof arg2 === "undefined" ? ffi.ptr(arg1) : ffi.ptr(arg1, arg2));
 const toBuffer = ffi.toBuffer;
 const toArrayBuffer = ffi.toArrayBuffer;
-const viewSource = ffi.viewSource;
+const nativeViewSource = ffi.viewSource;
 
 const BunCString = ffi.CString;
 const nativeLinkSymbols = ffi.linkSymbols;
@@ -81,7 +81,9 @@ delete ffi.closeCallback;
 
 class JSCallback {
   constructor(cb, options) {
-    const { ctx, ptr } = nativeCallback(options, cb);
+    const result = nativeCallback(options, cb);
+    if (Error.isError(result)) throw result;
+    const { ctx, ptr } = result;
     this.#ctx = ctx;
     this.ptr = ptr;
     this.#threadsafe = !!options?.threadsafe;
@@ -521,6 +523,12 @@ function cc(options) {
   return result;
 }
 
+function viewSource(symbols, isCallback?) {
+  const result = nativeViewSource(symbols, isCallback);
+  if (Error.isError(result)) throw result;
+  return result;
+}
+
 function linkSymbols(options) {
   const result = nativeLinkSymbols(options);
   if (Error.isError(result)) throw result;
diff --git a/test/js/bun/ffi/ffi-viewSource-non-object.test.ts b/test/js/bun/ffi/ffi-viewSource-non-object.test.ts
index a875ab7e3499..48ea21ad60a5 100644
--- a/test/js/bun/ffi/ffi-viewSource-non-object.test.ts
+++ b/test/js/bun/ffi/ffi-viewSource-non-object.test.ts
@@ -1,16 +1,81 @@
+import { JSCallback, viewSource } from "bun:ffi";
 import { describe, expect, test } from "bun:test";
 import { isArm64, isWindows } from "harness";
 
 const isFFIUnavailable = isWindows && isArm64;
 
+// Captures what a call throws, or undefined if it returned normally. Written
+// explicitly so the assertions below distinguish a thrown Error from a
+// returned one regardless of toThrow()'s handling of returned Errors.
+function thrown(fn: () => unknown): unknown {
+  try {
+    fn();
+  } catch (e) {
+    return e;
+  }
+  return undefined;
+}
+
 describe.skipIf(isFFIUnavailable)("FFI viewSource", () => {
-  test("rejects non-object symbol descriptor values", () => {
-    // These should throw a TypeError because each symbol descriptor
-    // must be an object like { args: [...], returns: "void" }.
-    // Previously, non-object values like numbers or strings would
-    // cause a debug assertion failure (crash) in generateSymbolForFunction.
-    expect(() => Bun.FFI.viewSource({ myFunc: 42 })).toThrow("Expected an object");
-    expect(() => Bun.FFI.viewSource({ myFunc: "not_an_object" })).toThrow("Expected an object");
-    expect(() => Bun.FFI.viewSource({ myFunc: true })).toThrow("Expected an object");
+  // Descriptor values must be objects like { args: [...], returns: "void" }.
+  // https://github.com/oven-sh/bun/pull/28361, https://github.com/oven-sh/bun/pull/34396
+  test.each([42, "not_an_object", true])("throws on non-object symbol descriptor value %p", value => {
+    const err = thrown(() => viewSource({ myFunc: value as any }));
+    expect(err).toBeInstanceOf(TypeError);
+    expect((err as TypeError).message).toContain("Expected an object");
+  });
+
+  test("throws on an unknown FFI type", () => {
+    const err = thrown(() => viewSource({ foo: { args: ["bogus_type" as any], returns: "void" } }));
+    expect(err).toBeInstanceOf(TypeError);
+    expect((err as TypeError).message).toContain("bogus_type");
+  });
+
+  test.each([null, undefined, 42])("throws on non-object options argument %p", value => {
+    const err = thrown(() => viewSource(value as any));
+    expect(err).toBeInstanceOf(TypeError);
+  });
+
+  test.each([null, undefined, 42, "str"])("throws on non-object callback descriptor %p", value => {
+    const err = thrown(() => viewSource(value as any, true));
+    expect(err).toBeInstanceOf(TypeError);
+    expect((err as TypeError).message).toContain("Expected an object");
+  });
+
+  test("returns the generated source for a valid descriptor", () => {
+    const src = viewSource({ foo: { args: ["i32"], returns: "i32" } });
+    expect(src).toBeArray();
+    expect(src).toHaveLength(1);
+    expect(src[0]).toContain("JSFunctionCall");
+
+    const cbSrc = viewSource({ args: ["i32"], returns: "i32" }, true);
+    expect(typeof cbSrc).toBe("string");
+    expect(cbSrc).toContain("my_callback_function");
+  });
+});
+
+describe.skipIf(isFFIUnavailable)("FFI JSCallback", () => {
+  test.each([null, undefined, 42, "str", true])("throws on non-object options %p", value => {
+    const err = thrown(() => new JSCallback(() => {}, value as any));
+    expect(err).toBeInstanceOf(TypeError);
+    expect((err as TypeError).message).toContain("Expected object");
+  });
+
+  test.each([null, undefined, 42, "str", {}])("throws on non-callable callback %p", value => {
+    const err = thrown(() => new JSCallback(value as any, { returns: "void" }));
+    expect(err).toBeInstanceOf(TypeError);
+    expect((err as TypeError).message).toContain("Expected callback function");
+  });
+
+  test("throws on an unknown FFI type", () => {
+    const err = thrown(() => new JSCallback(() => {}, { args: ["bogus_type" as any], returns: "void" }));
+    expect(err).toBeInstanceOf(TypeError);
+    expect((err as TypeError).message).toContain("bogus_type");
+  });
+
+  test("constructs with a valid descriptor", () => {
+    using cb = new JSCallback(() => {}, { args: ["i32"], returns: "void" });
+    expect(typeof cb.ptr).toBe("number");
+    expect(cb.ptr).not.toBe(0);
   });
 });