diff --git a/index.js b/index.js
index 9ec1b2fc..4bf2bc19 100644
--- a/index.js
+++ b/index.js
@@ -232,7 +232,10 @@ class Ky {
 		this.request = new globalThis.Request(this._input, this._options);
 
 		if (this._options.searchParams) {
-			const searchParams = '?' + new URLSearchParams(this._options.searchParams).toString();
+			const textSearchParams = typeof this._options.searchParams === 'string' ?
+				this._options.searchParams.replace(/^\?/, '') :
+				new URLSearchParams(this._options.searchParams).toString();
+			const searchParams = '?' + textSearchParams;
 			const url = this.request.url.replace(/(?:\?.*?)?(?=#|$)/, searchParams);
 
 			// To provide correct form boundary, Content-Type header should be deleted each time when new Request instantiated from another one
diff --git a/test/fetch.js b/test/fetch.js
index 98b7844f..3829d6b2 100644
--- a/test/fetch.js
+++ b/test/fetch.js
@@ -10,9 +10,9 @@ test.serial('relative URLs are passed to fetch unresolved', async t => {
 
 	t.is(await ky('/unicorn').text(), '/unicorn');
 	t.is(await ky('/unicorn', {searchParams: {foo: 'bar'}}).text(), '/unicorn?foo=bar');
-	t.is(await ky('/unicorn#hash', {searchParams: 'foo'}).text(), '/unicorn?foo=#hash');
-	t.is(await ky('/unicorn?old', {searchParams: 'new'}).text(), '/unicorn?new=');
-	t.is(await ky('/unicorn?old#hash', {searchParams: 'new'}).text(), '/unicorn?new=#hash');
+	t.is(await ky('/unicorn#hash', {searchParams: 'foo'}).text(), '/unicorn?foo#hash');
+	t.is(await ky('/unicorn?old', {searchParams: 'new'}).text(), '/unicorn?new');
+	t.is(await ky('/unicorn?old#hash', {searchParams: 'new'}).text(), '/unicorn?new#hash');
 	t.is(await ky('unicorn', {prefixUrl: '/api/'}).text(), '/api/unicorn');
 	globalThis.fetch = originalFetch;
 });
@@ -27,8 +27,8 @@ test('fetch option takes a custom fetch function', async t => {
 
 	t.is(await ky('/unicorn', {fetch: customFetch}).text(), '/unicorn');
 	t.is(await ky('/unicorn', {fetch: customFetch, searchParams: {foo: 'bar'}}).text(), '/unicorn?foo=bar');
-	t.is(await ky('/unicorn#hash', {fetch: customFetch, searchParams: 'foo'}).text(), '/unicorn?foo=#hash');
-	t.is(await ky('/unicorn?old', {fetch: customFetch, searchParams: 'new'}).text(), '/unicorn?new=');
-	t.is(await ky('/unicorn?old#hash', {fetch: customFetch, searchParams: 'new'}).text(), '/unicorn?new=#hash');
+	t.is(await ky('/unicorn#hash', {fetch: customFetch, searchParams: 'foo'}).text(), '/unicorn?foo#hash');
+	t.is(await ky('/unicorn?old', {fetch: customFetch, searchParams: 'new'}).text(), '/unicorn?new');
+	t.is(await ky('/unicorn?old#hash', {fetch: customFetch, searchParams: 'new'}).text(), '/unicorn?new#hash');
 	t.is(await ky('unicorn', {fetch: customFetch, prefixUrl: '/api/'}).text(), '/api/unicorn');
 });
diff --git a/test/main.js b/test/main.js
index b7e8aded..b3733125 100644
--- a/test/main.js
+++ b/test/main.js
@@ -341,11 +341,13 @@ test('searchParams option', async t => {
 	};
 	const searchParameters = new URLSearchParams(arrayParameters);
 	const stringParameters = '?cats=meow&dogs=true&opossums=false';
+	const customStringParameters = '?cats&dogs[0]=true&dogs[1]=false';
 
 	t.is(await ky(server.url, {searchParams: arrayParameters}).text(), stringParameters);
 	t.is(await ky(server.url, {searchParams: objectParameters}).text(), stringParameters);
 	t.is(await ky(server.url, {searchParams: searchParameters}).text(), stringParameters);
 	t.is(await ky(server.url, {searchParams: stringParameters}).text(), stringParameters);
+	t.is(await ky(server.url, {searchParams: customStringParameters}).text(), customStringParameters);
 
 	await server.close();
 });