diff --git a/src/bun.js/bindings/webcore/JSURLSearchParams.cpp b/src/bun.js/bindings/webcore/JSURLSearchParams.cpp
index 5db61d5d94..9a9f8083b5 100644
--- a/src/bun.js/bindings/webcore/JSURLSearchParams.cpp
+++ b/src/bun.js/bindings/webcore/JSURLSearchParams.cpp
@@ -123,7 +123,7 @@ template<> JSC::EncodedJSValue JSC_HOST_CALL_ATTRIBUTES JSURLSearchParamsDOMCons
     auto* castedThis = jsCast<JSURLSearchParamsDOMConstructor*>(callFrame->jsCallee());
     ASSERT(castedThis);
     EnsureStillAliveScope argument0 = callFrame->argument(0);
-    auto init = argument0.value().isUndefined() ? emptyString() : convert<IDLUnion<IDLSequence<IDLSequence<IDLUSVString>>, IDLRecord<IDLUSVString, IDLUSVString>, IDLUSVString>>(*lexicalGlobalObject, argument0.value());
+    auto init = argument0.value().isUndefinedOrNull() ? emptyString() : convert<IDLUnion<IDLSequence<IDLSequence<IDLUSVString>>, IDLRecord<IDLUSVString, IDLUSVString>, IDLUSVString>>(*lexicalGlobalObject, argument0.value());
     RETURN_IF_EXCEPTION(throwScope, {});
     auto object = URLSearchParams::create(WTFMove(init));
     if constexpr (IsExceptionOr<decltype(object)>)
diff --git a/test/js/node/test/parallel/test-whatwg-url-custom-searchparams-constructor.js b/test/js/node/test/parallel/test-whatwg-url-custom-searchparams-constructor.js
new file mode 100644
index 0000000000..a4c9eafab4
--- /dev/null
+++ b/test/js/node/test/parallel/test-whatwg-url-custom-searchparams-constructor.js
@@ -0,0 +1,92 @@
+// Tests below are not from WPT.
+
+require("../common");
+const assert = require("assert");
+
+function makeIterableFunc(array) {
+  return Object.assign(() => {}, {
+    [Symbol.iterator]() {
+      return array[Symbol.iterator]();
+    },
+  });
+}
+
+{
+  const iterableError = {
+    code: "ERR_ARG_NOT_ITERABLE",
+    name: "TypeError",
+    message: "Query pairs must be iterable",
+  };
+  const tupleError = {
+    code: "ERR_INVALID_TUPLE",
+    name: "TypeError",
+    message: "Each query pair must be an iterable [name, value] tuple",
+  };
+
+  let params;
+  params = new URLSearchParams(undefined);
+  assert.strictEqual(params.toString(), "");
+  params = new URLSearchParams(null);
+  assert.strictEqual(params.toString(), "");
+  params = new URLSearchParams(
+    makeIterableFunc([
+      ["key", "val"],
+      ["key2", "val2"],
+    ]),
+  );
+  assert.strictEqual(params.toString(), "key=val&key2=val2");
+  params = new URLSearchParams(
+    makeIterableFunc(
+      [
+        ["key", "val"],
+        ["key2", "val2"],
+      ].map(makeIterableFunc),
+    ),
+  );
+  assert.strictEqual(params.toString(), "key=val&key2=val2");
+  params = new URLSearchParams({ hasOwnProperty: 1 });
+  assert.strictEqual(params.get("hasOwnProperty"), "1");
+  assert.strictEqual(params.toString(), "hasOwnProperty=1");
+  assert.throws(() => new URLSearchParams([[1]]), tupleError);
+  assert.throws(() => new URLSearchParams([[1, 2, 3]]), tupleError);
+  assert.throws(() => new URLSearchParams({ [Symbol("test")]: 42 }), TypeError);
+  assert.throws(
+    () => new URLSearchParams({ [Symbol.iterator]: 42 }),
+    iterableError,
+  );
+  assert.throws(() => new URLSearchParams([{}]), tupleError);
+  assert.throws(() => new URLSearchParams(["a"]), tupleError);
+  assert.throws(() => new URLSearchParams([null]), tupleError);
+  assert.throws(
+    () => new URLSearchParams([{ [Symbol.iterator]: 42 }]),
+    tupleError,
+  );
+
+  assert.throws(
+    () => new URLSearchParams(makeIterableFunc([["key", "val", "val2"]])),
+    tupleError,
+  );
+}
+
+{
+  const obj = {
+    toString() {
+      throw new Error("toString");
+    },
+    valueOf() {
+      throw new Error("valueOf");
+    },
+  };
+  const sym = Symbol();
+  const toStringError = /^Error: toString$/;
+  const symbolError = /^TypeError: Cannot convert a Symbol value to a string$/;
+
+  assert.throws(() => new URLSearchParams({ a: obj }), toStringError);
+  assert.throws(() => new URLSearchParams([["a", obj]]), toStringError);
+  assert.throws(() => new URLSearchParams(sym), symbolError);
+  assert.throws(() => new URLSearchParams({ [sym]: "a" }), symbolError);
+  assert.throws(() => new URLSearchParams({ a: sym }), symbolError);
+  assert.throws(() => new URLSearchParams([[sym, "a"]]), symbolError);
+  assert.throws(() => new URLSearchParams([["a", sym]]), symbolError);
+}
+