diff --git a/packages/core/src/utils/eventbuilder.ts b/packages/core/src/utils/eventbuilder.ts
index 9b300c59c593..2e8445ed5878 100644
--- a/packages/core/src/utils/eventbuilder.ts
+++ b/packages/core/src/utils/eventbuilder.ts
@@ -7,10 +7,11 @@ import type { ParameterizedString } from '../types/parameterize';
 import type { SeverityLevel } from '../types/severity';
 import type { StackFrame } from '../types/stackframe';
 import type { StackParser } from '../types/stacktrace';
-import { isError, isErrorEvent, isParameterizedString, isPlainObject } from './is';
+import { isError, isErrorEvent, isParameterizedString, isPlainObject, isPrimitive } from './is';
 import { addExceptionMechanism, addExceptionTypeValue } from './misc';
-import { normalizeToSize } from './normalize';
+import { normalizeToSize, stringifyValue } from './normalize';
 import { extractExceptionKeysForMessage } from './object';
+import { stringify } from './string';
 
 /**
  * Extracts stack frames from the error.stack string
@@ -32,13 +33,40 @@ function hasSentryFetchUrlHost(error: unknown): error is Error & { __sentry_fetc
  * @hidden
  */
 export function _enhanceErrorWithSentryInfo<T extends Error>(error: T): string {
+  const message = errorMessageToString(error.message);
+
   // If the error has a __sentry_fetch_url_host__ property (added by fetch instrumentation),
   // enhance the error message with the hostname.
   if (hasSentryFetchUrlHost(error)) {
-    return `${error.message} (${error.__sentry_fetch_url_host__})`;
+    return `${message} (${error.__sentry_fetch_url_host__})`;
+  }
+
+  return message;
+}
+
+// `message` is typed as a string, but user code can assign anything to it, and event processors
+// call string methods on `exception.value`.
+function errorMessageToString(message: unknown): string {
+  if (typeof message === 'string') {
+    return message;
+  }
+
+  if (message == null) {
+    return '';
+  }
+
+  if (isPrimitive(message)) {
+    return String(message);
+  }
+
+  if (isPlainObject(message) || Array.isArray(message)) {
+    const json = stringify(message, '');
+    if (json) {
+      return json;
+    }
   }
 
-  return error.message;
+  return stringifyValue(undefined, message);
 }
 
 /**
diff --git a/packages/core/test/lib/utils/eventbuilder.test.ts b/packages/core/test/lib/utils/eventbuilder.test.ts
index 2a08f073117e..5a2fcc003419 100644
--- a/packages/core/test/lib/utils/eventbuilder.test.ts
+++ b/packages/core/test/lib/utils/eventbuilder.test.ts
@@ -308,5 +308,46 @@ describe('eventFromMessage', () => {
       const exception = exceptionFromError(stackParser, error);
       expect(exception.value).toBe('Failed to fetch (localhost:8080)');
     });
+
+    it('should enhance a non-string message', () => {
+      const error = new TypeError('placeholder');
+      (error as { message: unknown }).message = { code: 42 };
+      addNonEnumerableProperty(error, '__sentry_fetch_url_host__', 'example.com');
+
+      const exception = exceptionFromError(stackParser, error);
+      expect(exception.value).toBe('{"code":42} (example.com)');
+    });
+  });
+});
+
+describe('exceptionFromError', () => {
+  const circular: Record<string, unknown> = { code: 42 };
+  circular.self = circular;
+
+  it.each([
+    ['a number', 42, '42'],
+    ['a bigint', BigInt(42), '42'],
+    ['a boolean', false, 'false'],
+    ['undefined', undefined, ''],
+    ['null', null, ''],
+    ['an object', { code: 42 }, '{"code":42}'],
+    ['an array', [1, 'two'], '[1,"two"]'],
+    ['a circular object', circular, '[object Object]'],
+    ['a function', function namedFn() {}, '[Function: namedFn]'],
+    ['an error', new Error('inner'), '[object Error]'],
+    ['a map', new Map([['code', 42]]), '[object Map]'],
+    [
+      'a class instance',
+      new (class CustomMessage {
+        code = 42;
+      })(),
+      '{"code":42}',
+    ],
+  ])('turns %s into a string', (_, message, expected) => {
+    const error = new Error('placeholder');
+    (error as { message: unknown }).message = message;
+
+    const exception = exceptionFromError(stackParser, error);
+    expect(exception.value).toBe(expected);
   });
 });