diff --git a/lib/internal/url.js b/lib/internal/url.js
index 23340a3e5c1a01..0d34bcfd76a4a6 100644
--- a/lib/internal/url.js
+++ b/lib/internal/url.js
@@ -2,6 +2,7 @@
 
 const {
   Array,
+  ArrayIsArray,
   ArrayPrototypeJoin,
   ArrayPrototypeMap,
   ArrayPrototypePush,
@@ -211,7 +212,17 @@ class URLSearchParams {
           const desc = ReflectGetOwnPropertyDescriptor(init, key);
           if (desc !== undefined && desc.enumerable) {
             const typedKey = toUSVString(key);
-            const typedValue = toUSVString(init[key]);
+            let typedValue = '';
+            if (ArrayIsArray(init[key])) {
+              const len = init[key].length;
+              for (let j = 0; j < len; j++) {
+                typedValue += toUSVString(init[key][j]);
+                if (j < len - 1)
+                  typedValue += ',';
+              }
+            } else {
+              typedValue = toUSVString(init[key]);
+            }
 
             // Two different key may result same after `toUSVString()`, we only
             // leave the later one. Refers to WPT.
@@ -1017,12 +1028,17 @@ function serializeParams(array) {
 
   const firstEncodedParam = encodeStr(array[0], noEscape, paramHexTable);
   const firstEncodedValue = encodeStr(array[1], noEscape, paramHexTable);
-  let output = `${firstEncodedParam}=${firstEncodedValue}`;
+  let output = firstEncodedParam;
+  output += '=';
+  output += firstEncodedValue;
 
   for (let i = 2; i < len; i += 2) {
     const encodedParam = encodeStr(array[i], noEscape, paramHexTable);
     const encodedValue = encodeStr(array[i + 1], noEscape, paramHexTable);
-    output += `&${encodedParam}=${encodedValue}`;
+    output += '&';
+    output += encodedParam;
+    output += '=';
+    output += encodedValue;
   }
 
   return output;
diff --git a/lib/internal/util.js b/lib/internal/util.js
index 5665923a2cd297..c51209e61d76d9 100644
--- a/lib/internal/util.js
+++ b/lib/internal/util.js
@@ -72,7 +72,7 @@ const colorRegExp = /\u001b\[\d\d?m/g; // eslint-disable-line no-control-regex
 const unpairedSurrogateRe =
   /(?:[^\uD800-\uDBFF]|^)[\uDC00-\uDFFF]|[\uD800-\uDBFF](?![\uDC00-\uDFFF])/;
 function toUSVString(val) {
-  const str = `${val}`;
+  const str = '' + val;
   // As of V8 5.5, `str.search()` (and `unpairedSurrogateRe[@@search]()`) are
   // slower than `unpairedSurrogateRe.exec()`.
   const match = RegExpPrototypeExec(unpairedSurrogateRe, str);