diff --git a/cli/rt/11_url.js b/cli/rt/11_url.js
index 5de6cc8c73..86dcbf26d3 100644
--- a/cli/rt/11_url.js
+++ b/cli/rt/11_url.js
@@ -14,6 +14,10 @@
     return sendSync("op_domain_to_ascii", { domain, beStrict });
   }
 
+  function decodeSearchParam(p) {
+    return decodeURIComponent(p.replace(/\+/g, " "));
+  }
+
   const urls = new WeakMap();
 
   class URLSearchParams {
@@ -63,7 +67,7 @@
         const position = pair.indexOf("=");
         const name = pair.slice(0, position === -1 ? pair.length : position);
         const value = pair.slice(name.length + 1);
-        this.#append(decodeURIComponent(name), decodeURIComponent(value));
+        this.#append(decodeSearchParam(name), decodeSearchParam(value));
       }
     };
 
diff --git a/cli/tests/unit/url_search_params_test.ts b/cli/tests/unit/url_search_params_test.ts
index c20db56dd2..5e1d2afb53 100644
--- a/cli/tests/unit/url_search_params_test.ts
+++ b/cli/tests/unit/url_search_params_test.ts
@@ -48,6 +48,13 @@ unitTest(function urlSearchParamsInitString(): void {
   );
 });
 
+unitTest(function urlSearchParamsInitStringWithPlusCharacter(): void {
+  const init = "q=a+b";
+  const searchParams = new URLSearchParams(init);
+  assertEquals(searchParams.toString(), init);
+  assertEquals(searchParams.get("q"), "a b");
+});
+
 unitTest(function urlSearchParamsInitIterable(): void {
   const init = [
     ["a", "54"],