diff --git a/README.md b/README.md
index 5b05b71..a0ced06 100644
--- a/README.md
+++ b/README.md
@@ -55,8 +55,8 @@ Returns an iterator over all domains currently stored cookies for.
 #### *cookiesDomain(domain)
 Returns an iterator over all cookies currently stored for `domain`.
 
-#### *cookiesValid()
-Returns an iterator over all valid (non-expired) cookies.
+#### *cookiesValid(withSession)
+Returns an iterator over all valid (non-expired) cookies. Includes session cookies if `withSession` is `true`.
 
 #### *cookiesAll()
 Returns an iterator over all cookies currently stored.
@@ -65,10 +65,10 @@ Returns an iterator over all cookies currently stored.
 Returns an iterator over all cookies valid for a request to `url`.
 
 #### deleteExpired()
-Removes all expired cookies from the jar.
+Removes all expired cookies from the jar (including session cookies).
 
 #### save()
-Saves the cookie jar to disk. Only non-expired cookies are saved.
+Saves the cookie jar to disk. Only non-expired non-session cookies are saved.
 
 
 ### Class: Cookie
@@ -77,11 +77,11 @@ An abstract representation of a cookie.
 #### Properties
 - `name` The identifier of the cookie.
 - `value` The value of the cookie.
-- `expiry` A [Date](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date) object of the cookies expiry date.
+- `expiry` A [Date](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date) object of the cookies expiry date or `null`, if the cookie expires with the session.
 - `domain` The domain the cookie is valid for.
 - `path` The path the cookie is valid for.
 - `secure` A boolean value representing the cookie's secure attribute. If set the cookie will only be used for `https` requests.
-- `subdomains` A boolean value specifying whether the cookie should be used for subdomains of the domain or not.
+- `subdomains` A boolean value specifying whether the cookie should be used for requests to subdomains of `domain` or not.
 
 #### new Cookie(cookie, url)
 - `cookie` The string representation of a cookie as send by a webserver.
@@ -93,8 +93,8 @@ Creates a cookie instance from an already existing object with the same properti
 #### serialize()
 Serializes the cookie, transforming it to `name=value` so it can be used in requests.
 
-#### hasExpired()
-Returns whether the cookie has expired or not.
+#### hasExpired(sessionEnded)
+Returns whether the cookie has expired or not. `sessionEnded` specifies whether the current session has ended, meaning if set to `true`, the function will return `true` for session cookies.
 
 #### isValidForRequest(url)
 Returns whether the cookie is valid for a request to `url`. If not, it won't be send by the fetch wrapper.
diff --git a/src/cookie-jar.mjs b/src/cookie-jar.mjs
index 81c3e4d..cf6ec2f 100644
--- a/src/cookie-jar.mjs
+++ b/src/cookie-jar.mjs
@@ -45,9 +45,9 @@ export default class CookieJar {
         for(const cookie of (this.cookies.get(domain) || []).values())
             yield cookie;
     }
-    *cookiesValid() {
+    *cookiesValid(withSession) {
         for(const cookie of this.cookiesAll())
-            if(!cookie.hasExpired())
+            if(!cookie.hasExpired(!withSession))
                 yield cookie;
     }
     *cookiesAll() {
@@ -73,7 +73,7 @@ export default class CookieJar {
         }
     }
     deleteExpired() {
-        const validCookies = [...this.cookiesValid()];
+        const validCookies = [...this.cookiesValid(false)];
         this.cookies = new Map();
         validCookies.forEach(c => this.addCookie(c));
     }
@@ -81,6 +81,6 @@ export default class CookieJar {
         if(typeof this.file !== "string")
             throw new Error("No file has been specified for this cookie jar!");
         // only save cookies that haven't expired
-        fs.writeFileSync(this.file, JSON.stringify([...this.cookiesValid()]));
+        fs.writeFileSync(this.file, JSON.stringify([...this.cookiesValid(false)]));
     }
 };
diff --git a/src/cookie.mjs b/src/cookie.mjs
index b04b76f..8aeeca8 100644
--- a/src/cookie.mjs
+++ b/src/cookie.mjs
@@ -109,11 +109,11 @@ export default class Cookie {
     serialize() {
         return this.name + "=" + this.value;
     }
-    hasExpired() {
-        return this.expiry && this.expiry < new Date();
+    hasExpired(sessionEnded) {
+        return sessionEnded && this.expiry === null || this.expiry < new Date();
     }
     isValidForRequest(requestURL) {
-        if(this.hasExpired())
+        if(this.hasExpired(false))
             return false;
         const parsedURL = url.parse(requestURL);
         if(parsedURL.protocol !== "http:" && parsedURL.protocol !== "https:"