diff --git a/README.md b/README.md
index 8a45371..6a7f06f 100644
--- a/README.md
+++ b/README.md
@@ -33,12 +33,12 @@ A class that stores cookies.
 - `file` The path of the cookie jar on the disk.
 - `cookies` A [Map](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map) mapping cookie names to their properties.
 
-#### new CookieJar(flags, file[, cookies])
+#### new CookieJar(flags[, file, cookies])
 - `flags` A string specifying whether cookies should be read and/or written from/to the jar when passing it as parameter to [fetch](#fetchcookiejar-url-options).
     - `r`: only read from this jar
     - `w`: only write to this jar
     - `rw` or `wr`: read/write from/to this jar
-- `file` A string containing a relative or absolute path to the file on the disk to use.
+- `file` An optional string containing a relative or absolute path to the file on the disk to use.
 - `cookies` An optional initializer for the cookie jar - either an array of [Cookie](#class-cookie) instances or a single Cookie instance.
 
 #### addCookie(cookie[, url])
diff --git a/src/cookie-jar.mjs b/src/cookie-jar.mjs
index 550bbf3..c842d2f 100644
--- a/src/cookie-jar.mjs
+++ b/src/cookie-jar.mjs
@@ -8,7 +8,7 @@ export default class CookieJar {
         this.flags = flags;
         if(typeof this.flags !== "string")
             throw new TypeError("First parameter is not a string!");
-        if(typeof this.file !== "string")
+        if(this.file && typeof this.file !== "string")
             throw new TypeError("Second parameter is not a string!");
         if(Array.isArray(cookies)) {
             if(!cookies.every(c => c instanceof Cookie))
@@ -20,7 +20,7 @@ export default class CookieJar {
             this.cookies.set(cookies.name, cookies);
         else if(cookies)
             throw new TypeError("Third parameter is neither an array nor a cookie!");
-        if(this.cookies.size === 0 && this.file.length !== 0 && fs.existsSync(this.file))
+        if(this.file && this.cookies.size === 0 && this.file.length !== 0 && fs.existsSync(this.file))
             this.cookies = new Map(JSON.parse(fs.readFileSync(this.file)).map(([k, v]) => [k, Cookie.fromObject(v)]));
     }
     addCookie(c, fromURL) {
@@ -32,6 +32,8 @@ export default class CookieJar {
         this.cookies.forEach(callback);
     }
     save() {
+        if(typeof this.file !== "string")
+            throw new Error("No file has been specified for this cookie jar!");
         // only save cookies that haven't expired
         let cookiesToSave = new Map();
         this.forEach(cookie => {