diff --git a/packages/nuqs/src/serializer.test.ts b/packages/nuqs/src/serializer.test.ts
index 5ef06ae5..0f6573b9 100644
--- a/packages/nuqs/src/serializer.test.ts
+++ b/packages/nuqs/src/serializer.test.ts
@@ -1,4 +1,4 @@
-import { describe, expect, test } from 'vitest'
+import { describe, expect, it } from 'vitest'
 import type { Options } from './defs'
 import {
   parseAsArrayOf,
@@ -16,91 +16,91 @@ const parsers = {
 }
 
 describe('serializer', () => {
-  test('empty', () => {
+  it('handles empty inputs', () => {
     const serialize = createSerializer(parsers)
     const result = serialize({})
     expect(result).toBe('')
   })
-  test('one item', () => {
+  it('handles a single item', () => {
     const serialize = createSerializer(parsers)
     const result = serialize({ str: 'foo' })
     expect(result).toBe('?str=foo')
   })
-  test('several items', () => {
+  it('handles several items', () => {
     const serialize = createSerializer(parsers)
     const result = serialize({ str: 'foo', int: 1, bool: true })
     expect(result).toBe('?str=foo&int=1&bool=true')
   })
-  test("null items don't show up", () => {
+  it('does not render null items', () => {
     const serialize = createSerializer(parsers)
     const result = serialize({ str: null })
     expect(result).toBe('')
   })
-  test('with string base', () => {
+  it('handles a string base', () => {
     const serialize = createSerializer(parsers)
     const result = serialize('/foo', { str: 'foo' })
     expect(result).toBe('/foo?str=foo')
   })
-  test('with string base with search params', () => {
+  it('handles a string base with search params', () => {
     const serialize = createSerializer(parsers)
     const result = serialize('/foo?bar=egg', { str: 'foo' })
     expect(result).toBe('/foo?bar=egg&str=foo')
   })
-  test('with URLSearchParams base', () => {
+  it('handles a URLSearchParams base', () => {
     const serialize = createSerializer(parsers)
     const search = new URLSearchParams('?bar=egg')
     const result = serialize(search, { str: 'foo' })
     expect(result).toBe('?bar=egg&str=foo')
   })
-  test('Does not mutate existing params with URLSearchParams base', () => {
+  it('does not mutate existing params with URLSearchParams base', () => {
     const serialize = createSerializer(parsers)
     const searchBefore = new URLSearchParams('?str=foo')
     const result = serialize(searchBefore, { str: 'bar' })
     expect(result).toBe('?str=bar')
     expect(searchBefore.get('str')).toBe('foo')
   })
-  test('with URL base', () => {
+  it('handles a URL base', () => {
     const serialize = createSerializer(parsers)
     const url = new URL('https://example.com/path')
     const result = serialize(url, { str: 'foo' })
     expect(result).toBe('https://example.com/path?str=foo')
   })
-  test('with URL base and search params', () => {
+  it('handles a URL base and merges search params', () => {
     const serialize = createSerializer(parsers)
     const url = new URL('https://example.com/path?bar=egg')
     const result = serialize(url, { str: 'foo' })
     expect(result).toBe('https://example.com/path?bar=egg&str=foo')
   })
-  test('null value deletes from base', () => {
+  it('deletes a null value from base', () => {
     const serialize = createSerializer(parsers)
     const result = serialize('?str=bar&int=-1', { str: 'foo', int: null })
     expect(result).toBe('?str=foo')
   })
-  test('null deletes all from base', () => {
+  it('deletes all from base with a global null', () => {
     const serialize = createSerializer(parsers)
     const result = serialize('?str=bar&int=-1', null)
     expect(result).toBe('')
   })
-  test('null keeps search params not managed by the serializer', () => {
+  it('keeps search params not managed by the serializer when fed null', () => {
     const serialize = createSerializer(parsers)
     const result = serialize('?str=foo&external=kept', null)
     expect(result).toBe('?external=kept')
   })
-  test('clears value when setting null for search param that has a default value', () => {
+  it('clears value when setting null for a search param that has a default value', () => {
     const serialize = createSerializer({
       int: parseAsInteger.withDefault(0)
     })
     const result = serialize('?int=1&str=foo', { int: null })
     expect(result).toBe('?str=foo')
   })
-  test('clears value when setting null for search param that is set to its default value', () => {
+  it('clears value when setting null for æ search param that is set to its default value', () => {
     const serialize = createSerializer({
       int: parseAsInteger.withDefault(0)
     })
     const result = serialize('?int=0&str=foo', { int: null })
     expect(result).toBe('?str=foo')
   })
-  test('clears value when setting the default value (`clearOnDefault: true` is the default)', () => {
+  it('clears value when setting the default value (`clearOnDefault: true` is the default)', () => {
     const serialize = createSerializer({
       int: parseAsInteger.withDefault(0),
       str: parseAsString.withDefault(''),
@@ -117,7 +117,7 @@ describe('serializer', () => {
     })
     expect(result).toBe('')
   })
-  test('keeps value when setting the default value when `clearOnDefault: false`', () => {
+  it('keeps value when setting the default value when `clearOnDefault: false`', () => {
     const options: Options = { clearOnDefault: false }
     const serialize = createSerializer({
       int: parseAsInteger.withOptions(options).withDefault(0),
@@ -139,7 +139,7 @@ describe('serializer', () => {
       '?int=0&str=&bool=false&arr=&json={%22foo%22:%22bar%22}'
     )
   })
-  test('support for global clearOnDefault option', () => {
+  it('supports a global clearOnDefault option', () => {
     const serialize = createSerializer(
       {
         int: parseAsInteger.withDefault(0),
@@ -161,7 +161,7 @@ describe('serializer', () => {
       '?int=0&str=&bool=false&arr=&json={%22foo%22:%22bar%22}'
     )
   })
-  test('parser clearOnDefault takes precedence over global clearOnDefault', () => {
+  it('gives precedence to parser clearOnDefault over global clearOnDefault', () => {
     const serialize = createSerializer(
       {
         int: parseAsInteger
@@ -177,7 +177,7 @@ describe('serializer', () => {
     })
     expect(result).toBe('?str=')
   })
-  test('supports urlKeys', () => {
+  it('supports urlKeys', () => {
     const serialize = createSerializer(parsers, {
       urlKeys: {
         bool: 'b',
@@ -188,4 +188,17 @@ describe('serializer', () => {
     const result = serialize({ str: 'foo', int: 1, bool: true })
     expect(result).toBe('?s=foo&i=1&b=true')
   })
+  it('supports ? in the values', () => {
+    const serialize = createSerializer(parsers)
+    const result = serialize({ str: 'foo?bar', int: 1, bool: true })
+    expect(result).toBe('?str=foo?bar&int=1&bool=true')
+  })
+  it('supports & in the base', () => {
+    // Repro for https://github.com/47ng/nuqs/issues/812
+    const serialize = createSerializer(parsers)
+    const result = serialize('https://example.com/path?issue=is?here', {
+      str: 'foo?bar'
+    })
+    expect(result).toBe('https://example.com/path?issue=is?here&str=foo?bar')
+  })
 })
diff --git a/packages/nuqs/src/serializer.ts b/packages/nuqs/src/serializer.ts
index 272c05b1..bcb8665f 100644
--- a/packages/nuqs/src/serializer.ts
+++ b/packages/nuqs/src/serializer.ts
@@ -81,8 +81,8 @@ function isBase(base: any): base is Base {
 
 function splitBase(base: Base) {
   if (typeof base === 'string') {
-    const [path = '', search] = base.split('?')
-    return [path, new URLSearchParams(search)] as const
+    const [path = '', ...search] = base.split('?')
+    return [path, new URLSearchParams(search.join('?'))] as const
   } else if (base instanceof URLSearchParams) {
     return ['', new URLSearchParams(base)] as const // Operate on a copy of URLSearchParams, as derived classes may restrict its allowed methods
   } else {