diff --git a/src/utils.ts b/src/utils.ts
index ae60d2be..7ea72b9f 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -456,7 +456,10 @@ export function withoutProtocol(input: string): string {
  * @group utils
  */
 export function withProtocol(input: string, protocol: string): string {
-  const match = input.match(PROTOCOL_REGEX);
+  let match = input.match(PROTOCOL_REGEX);
+  if (!match) {
+    match = input.match(/^\/{2,}/);
+  }
   if (!match) {
     return protocol + input;
   }
diff --git a/test/utilities.test.ts b/test/utilities.test.ts
index c7fd0571..16c3f12d 100644
--- a/test/utilities.test.ts
+++ b/test/utilities.test.ts
@@ -178,6 +178,21 @@ describe("withHttps", () => {
 
 describe("withProtocol", () => {
   const tests = [
+    {
+      input: "example.com",
+      protocol: "https://",
+      out: "https://example.com",
+    },
+    {
+      input: "//example.com",
+      protocol: "https://",
+      out: "https://example.com",
+    },
+    {
+      input: "://example.com", // Malformed URL is considered without protocol
+      protocol: "https://",
+      out: "https://://example.com",
+    },
     {
       input: "http://example.com",
       protocol: "https://",