diff --git a/packages/cloudflare/src/vite/transform.ts b/packages/cloudflare/src/vite/transform.ts
index ad823b1f00c7..43e975782a2d 100644
--- a/packages/cloudflare/src/vite/transform.ts
+++ b/packages/cloudflare/src/vite/transform.ts
@@ -416,14 +416,69 @@ function wrapDefaultExport(node: ExportDefaultNode, ctx: TransformContext, state
     return;
   }
 
-  // `export default <expr>` → `const __SENTRY_DEFAULT_EXPORT__ = <expr>`
-  // MagicString positions are always relative to the original source.
-  state.ms.overwrite(node.start, decl.start, 'const __SENTRY_DEFAULT_EXPORT__ = ');
-  state.ms.append(`\nexport default __SENTRY__.withSentry(${state.optionsFn}, __SENTRY_DEFAULT_EXPORT__);\n`);
+  // MagicString positions are always relative to the original source. Only the `export default`
+  // keywords are replaced, so parentheses around the expression stay.
+  const source = state.ms.original;
+  const keywordsEnd = exportDefaultKeywordsEnd(source, node.start);
+  const declaredName =
+    decl.type === 'ClassDeclaration' || decl.type === 'FunctionDeclaration'
+      ? (decl as ClassDeclarationNode).id?.name
+      : undefined;
+
+  // As with `export { handler as default }`, the export is set in two steps: bound as-is where the
+  // original statement set it, then rebound at the end of the module to the wrapper, which sees
+  // methods added in between. See `wrapDefaultSpecifier`.
+  let wrapped = '__SENTRY_DEFAULT_EXPORT__';
+  if (declaredName) {
+    // `export default class Handler {}`: the declaration stays, so `Handler` stays bound in the module.
+    state.ms.remove(node.start, decl.start);
+    state.ms.appendLeft(node.end, `\nvar __SENTRY_DEFAULT_EXPORT__ = ${declaredName};`);
+    wrapped = declaredName;
+  } else if (isAnonymousFunctionOrClass(decl)) {
+    // As a property value, the class or function gets the name `default`, as `export default` gives it.
+    const hasSemicolon = source[node.end - 1] === ';';
+    state.ms.overwrite(node.start, keywordsEnd, 'var __SENTRY_DEFAULT_EXPORT__ = { default:');
+    state.ms.appendLeft(hasSemicolon ? node.end - 1 : node.end, hasSemicolon ? ' }.default' : ' }.default;');
+  } else {
+    state.ms.overwrite(node.start, keywordsEnd, 'var __SENTRY_DEFAULT_EXPORT__ =');
+  }
+  state.ms.appendLeft(node.end, '\nexport { __SENTRY_DEFAULT_EXPORT__ as default };');
+  state.ms.append(`\n__SENTRY_DEFAULT_EXPORT__ = __SENTRY__.withSentry(${state.optionsFn}, ${wrapped});`);
   state.needsImport = true;
   state.autoWrapped.add(DEFAULT_EXPORT);
 }
 
+/**
+ * Offset just past the `default` keyword of the `export default` statement at `start`. Comments can
+ * sit between `export`, `default` and the expression, and may themselves contain the word `default`.
+ */
+function exportDefaultKeywordsEnd(source: string, start: number): number {
+  let index = start + 'export'.length;
+  while (index < source.length && !source.startsWith('default', index)) {
+    if (source.startsWith('//', index)) {
+      const lineEnd = source.indexOf('\n', index);
+      index = lineEnd === -1 ? source.length : lineEnd;
+    } else if (source.startsWith('/*', index)) {
+      const commentEnd = source.indexOf('*/', index + 2);
+      index = commentEnd === -1 ? source.length : commentEnd + 2;
+    } else {
+      index++;
+    }
+  }
+  return index + 'default'.length;
+}
+
+function isAnonymousFunctionOrClass(node: BaseNode): boolean {
+  if (node.type === 'ArrowFunctionExpression') return true;
+  const isFunctionOrClass = [
+    'FunctionExpression',
+    'FunctionDeclaration',
+    'ClassExpression',
+    'ClassDeclaration',
+  ].includes(node.type);
+  return isFunctionOrClass && !(node as ClassDeclarationNode).id;
+}
+
 function handleNamedExport(node: ExportNamedNode, ctx: TransformContext, state: TransformState): void {
   const decl = node.declaration;
 
diff --git a/packages/cloudflare/test/vite/autoInstrument.test.ts b/packages/cloudflare/test/vite/autoInstrument.test.ts
index cb70d3533b80..379589698688 100644
--- a/packages/cloudflare/test/vite/autoInstrument.test.ts
+++ b/packages/cloudflare/test/vite/autoInstrument.test.ts
@@ -428,9 +428,9 @@ describe('wranglerConfigPath option', () => {
     expect(result.code).toBe(
       [
         "import * as __SENTRY__ from '@sentry/cloudflare';",
-        'const __SENTRY_DEFAULT_EXPORT__ = { fetch() { return new Response("ok"); } };',
-        'export default __SENTRY__.withSentry(() => undefined, __SENTRY_DEFAULT_EXPORT__);',
-        '',
+        'var __SENTRY_DEFAULT_EXPORT__ = { fetch() { return new Response("ok"); } };',
+        'export { __SENTRY_DEFAULT_EXPORT__ as default };',
+        '__SENTRY_DEFAULT_EXPORT__ = __SENTRY__.withSentry(() => undefined, __SENTRY_DEFAULT_EXPORT__);',
       ].join('\n'),
     );
   });
@@ -506,9 +506,9 @@ describe('package specifier as wrangler `main`', () => {
     expect(result.code).toBe(
       [
         "import * as __SENTRY__ from '@sentry/cloudflare';",
-        'const __SENTRY_DEFAULT_EXPORT__ = { fetch() { return new Response("ok"); } };',
-        'export default __SENTRY__.withSentry(() => undefined, __SENTRY_DEFAULT_EXPORT__);',
-        '',
+        'var __SENTRY_DEFAULT_EXPORT__ = { fetch() { return new Response("ok"); } };',
+        'export { __SENTRY_DEFAULT_EXPORT__ as default };',
+        '__SENTRY_DEFAULT_EXPORT__ = __SENTRY__.withSentry(() => undefined, __SENTRY_DEFAULT_EXPORT__);',
       ].join('\n'),
     );
   });
diff --git a/packages/cloudflare/test/vite/transform.test.ts b/packages/cloudflare/test/vite/transform.test.ts
index 5779fc489ce1..9fe5018a832d 100644
--- a/packages/cloudflare/test/vite/transform.test.ts
+++ b/packages/cloudflare/test/vite/transform.test.ts
@@ -52,7 +52,7 @@ describe('default export wrapping', () => {
     const result = transform(code, ctx)!;
     expect(result).toBeDefined();
     expect(result.code).toContain("import * as __SENTRY__ from '@sentry/cloudflare'");
-    expect(result.code).toContain('const __SENTRY_DEFAULT_EXPORT__ = handler');
+    expect(result.code).toContain('var __SENTRY_DEFAULT_EXPORT__ = handler');
     expect(result.code).toContain('__SENTRY__.withSentry((env) => ({}), __SENTRY_DEFAULT_EXPORT__)');
     expect(result.code).not.toContain('export default handler');
     expect(result.map).toBeDefined();
@@ -62,7 +62,7 @@ describe('default export wrapping', () => {
     const code = 'export default { fetch() { return new Response("ok"); } };';
     const result = transform(code, ctx)!;
     expect(result).toBeDefined();
-    expect(result.code).toContain('const __SENTRY_DEFAULT_EXPORT__ =');
+    expect(result.code).toContain('var __SENTRY_DEFAULT_EXPORT__ =');
     expect(result.code).toContain('__SENTRY__.withSentry(');
   });
 
@@ -286,6 +286,121 @@ describe('default export wrapping', () => {
     expect(result.code).toContain('tracesSampleRate: 1.0');
   });
 
+  /**
+   * Writes `files` to a temp dir, with `a.mjs` transformed and `withSentry` stubbed to mark each
+   * method it finds as instrumented, and returns what `node <entry>` prints.
+   */
+  function runWithEntry(files: Record<string, string>, entry: string, transformEntry = true): string {
+    const dir = mkdtempSync(join(tmpdir(), 'sentry-cf-default-'));
+    try {
+      for (const [name, code] of Object.entries(files)) {
+        const out =
+          name === 'a.mjs' && transformEntry
+            ? transform(code, ctx)!.code.replace(
+                "import * as __SENTRY__ from '@sentry/cloudflare';",
+                'const __SENTRY__ = { withSentry: (_options, handler) => { for (const key of Object.keys(handler)) handler[key].instrumented = true; return handler; } };',
+              )
+            : code;
+        writeFileSync(join(dir, name), out);
+      }
+      return execFileSync(process.execPath, [join(dir, entry)], { encoding: 'utf8' }).trim();
+    } finally {
+      rmSync(dir, { recursive: true, force: true });
+    }
+  }
+
+  it.each([
+    'export default class { fetch() {} }',
+    'export default function () {}',
+    'export default () => {};',
+    'export default (class { fetch() {} });',
+    'export default class Handler { fetch() {} }',
+    'export default function handler() {}',
+  ])('keeps the name of the default export of `%s`', code => {
+    const files = { 'a.mjs': code, 'b.mjs': "import handler from './a.mjs';\nconsole.log(handler.name);" };
+    expect(runWithEntry(files, 'b.mjs')).toBe(runWithEntry(files, 'b.mjs', false));
+  });
+
+  it('wraps a parenthesized default export', () => {
+    const code = ['const handler = { fetch() {} };', 'export default (handler);'].join('\n');
+
+    expect(transform(code, ctx)!.code).toBe(
+      [
+        "import * as __SENTRY__ from '@sentry/cloudflare';",
+        'const handler = { fetch() {} };',
+        'var __SENTRY_DEFAULT_EXPORT__ = (handler);',
+        'export { __SENTRY_DEFAULT_EXPORT__ as default };',
+        '__SENTRY_DEFAULT_EXPORT__ = __SENTRY__.withSentry((env) => ({}), __SENTRY_DEFAULT_EXPORT__);',
+      ].join('\n'),
+    );
+  });
+
+  it('wraps a default export with a comment that mentions `default`', () => {
+    const code = 'export /* the default */ default /* default handler */ { fetch() {} };';
+
+    expect(transform(code, ctx)!.code).toBe(
+      [
+        "import * as __SENTRY__ from '@sentry/cloudflare';",
+        'var __SENTRY_DEFAULT_EXPORT__ = /* default handler */ { fetch() {} };',
+        'export { __SENTRY_DEFAULT_EXPORT__ as default };',
+        '__SENTRY_DEFAULT_EXPORT__ = __SENTRY__.withSentry((env) => ({}), __SENTRY_DEFAULT_EXPORT__);',
+      ].join('\n'),
+    );
+  });
+
+  it('wraps a default export with a line comment that mentions `default`', () => {
+    const code = ['export // the default', 'default // default handler', '{ fetch() {} };'].join('\n');
+
+    expect(transform(code, ctx)!.code).toBe(
+      [
+        "import * as __SENTRY__ from '@sentry/cloudflare';",
+        'var __SENTRY_DEFAULT_EXPORT__ = // default handler',
+        '{ fetch() {} };',
+        'export { __SENTRY_DEFAULT_EXPORT__ as default };',
+        '__SENTRY_DEFAULT_EXPORT__ = __SENTRY__.withSentry((env) => ({}), __SENTRY_DEFAULT_EXPORT__);',
+      ].join('\n'),
+    );
+  });
+
+  it('keeps the module binding of a named default class', () => {
+    const code = ['export default class Handler { fetch() {} }', 'Handler.ready = true;'].join('\n');
+
+    expect(transform(code, ctx)!.code).toBe(
+      [
+        "import * as __SENTRY__ from '@sentry/cloudflare';",
+        'class Handler { fetch() {} }',
+        'var __SENTRY_DEFAULT_EXPORT__ = Handler;',
+        'export { __SENTRY_DEFAULT_EXPORT__ as default };',
+        'Handler.ready = true;',
+        '__SENTRY_DEFAULT_EXPORT__ = __SENTRY__.withSentry((env) => ({}), Handler);',
+      ].join('\n'),
+    );
+  });
+
+  it('wraps a method added to the default export after `export default`', () => {
+    const files = {
+      'a.mjs': ['const handler = {};', 'export default handler;', 'handler.fetch = function () {};'].join('\n'),
+      'main.mjs': "import handler from './a.mjs';\nconsole.log(String(handler.fetch.instrumented));",
+    };
+
+    expect(runWithEntry(files, 'main.mjs')).toBe('true');
+  });
+
+  it('sets the default export where the original statement set it', () => {
+    // `b` reads the default export of `a` while `a` is still evaluating, after its `export default`.
+    const files = {
+      'a.mjs': [
+        "import { readDefault } from './b.mjs';",
+        'export default { fetch() {} };',
+        'export const seen = readDefault();',
+      ].join('\n'),
+      'b.mjs': "import handler from './a.mjs';\nexport function readDefault() { return typeof handler.fetch; }",
+      'main.mjs': "import { seen } from './a.mjs';\nconsole.log(seen);",
+    };
+
+    expect(runWithEntry(files, 'main.mjs')).toBe('function');
+  });
+
   it('skips when already wrapped with withSentry', () => {
     const code = [
       "import { withSentry } from '@sentry/cloudflare';",
@@ -926,9 +1041,9 @@ describe('agent class wrapping', () => {
         'class __SENTRY_ORIGINAL_MyDO__ extends DurableObject {}',
         'export const MyDO = __SENTRY__.instrumentDurableObjectWithSentry((env) => ({ dsn: env.SENTRY_DSN }), __SENTRY_ORIGINAL_MyDO__);',
         '',
-        'const __SENTRY_DEFAULT_EXPORT__ = { fetch() {} };',
-        'export default __SENTRY__.withSentry((env) => ({ dsn: env.SENTRY_DSN }), __SENTRY_DEFAULT_EXPORT__);',
-        '',
+        'var __SENTRY_DEFAULT_EXPORT__ = { fetch() {} };',
+        'export { __SENTRY_DEFAULT_EXPORT__ as default };',
+        '__SENTRY_DEFAULT_EXPORT__ = __SENTRY__.withSentry((env) => ({ dsn: env.SENTRY_DSN }), __SENTRY_DEFAULT_EXPORT__);',
       ].join('\n'),
     );
   });
@@ -1034,8 +1149,8 @@ describe('combined transforms', () => {
     expect(result.code).toContain('export const MyDO = __SENTRY__.instrumentDurableObjectWithSentry(');
 
     // Default export wrapped
-    expect(result.code).toContain('const __SENTRY_DEFAULT_EXPORT__ =');
-    expect(result.code).toContain('export default __SENTRY__.withSentry(');
+    expect(result.code).toContain('var __SENTRY_DEFAULT_EXPORT__ =');
+    expect(result.code).toContain('__SENTRY_DEFAULT_EXPORT__ = __SENTRY__.withSentry(');
 
     // Single import
     const importCount = (result.code.match(/import \* as __SENTRY__/g) ?? []).length;