diff --git a/lib/cookie.ts b/lib/cookie.ts
index 50e90209..6f0abb67 100644
--- a/lib/cookie.ts
+++ b/lib/cookie.ts
@@ -39,6 +39,7 @@ import * as validators from './validators'
 import { version } from './version'
 import { permuteDomain } from './permuteDomain'
 import { getCustomInspectSymbol } from './utilHelper'
+import { ErrorCallback, safeToString } from './utils'
 
 // From RFC6265 S4.1.1
 // note that it excludes \x3B ";"
@@ -357,7 +358,7 @@ function parseDate(str: string | undefined | null): Date | undefined {
 }
 
 function formatDate(date: Date) {
-  validators.validate(validators.isDate(date), date)
+  validators.validate(validators.isDate(date), safeToString(date))
   return date.toUTCString()
 }
 
@@ -699,7 +700,7 @@ function parse(
  * @returns boolean
  */
 function isSecurePrefixConditionMet(cookie: Cookie) {
-  validators.validate(validators.isObject(cookie), cookie)
+  validators.validate(validators.isObject(cookie), safeToString(cookie))
   const startsWithSecurePrefix =
     typeof cookie.key === 'string' && cookie.key.startsWith('__Secure-')
   return !startsWithSecurePrefix || cookie.secure
@@ -786,8 +787,8 @@ function fromJSON(str: string | SerializedCookie | null | undefined) {
  */
 
 function cookieCompare(a: Cookie, b: Cookie) {
-  validators.validate(validators.isObject(a), a)
-  validators.validate(validators.isObject(b), b)
+  validators.validate(validators.isObject(a), safeToString(a))
+  validators.validate(validators.isObject(b), safeToString(b))
   let cmp = 0
 
   // descending for length: b CMP a
@@ -977,8 +978,11 @@ export class Cookie {
     ) {
       return false
     }
-    // @ts-ignore
-    if (this.maxAge != null && this.maxAge <= 0) {
+    if (
+      this.maxAge != null &&
+      this.maxAge !== 'Infinity' &&
+      (this.maxAge === '-Infinity' || this.maxAge <= 0)
+    ) {
       return false // "Max-Age=" non-zero-digit *DIGIT
     }
     if (this.path != null && !PATH_VALUE.test(this.path)) {
@@ -1343,7 +1347,11 @@ export class CookieJar {
     const promiseCallback = createPromiseCallback<Cookie>(arguments)
     const cb = promiseCallback.callback
 
-    validators.validate(validators.isNonEmptyString(url), callback, options)
+    validators.validate(
+      validators.isNonEmptyString(url),
+      callback,
+      safeToString(options),
+    )
     let err
 
     if (validators.isFunction(url)) {
@@ -1629,7 +1637,7 @@ export class CookieJar {
     if (typeof options === 'function' || options === undefined) {
       options = defaultGetCookieOptions
     }
-    validators.validate(validators.isObject(options), cb, options)
+    validators.validate(validators.isObject(options), cb, safeToString(options))
     validators.validate(validators.isFunction(cb), cb)
 
     const host = canonicalDomain(context.hostname)
@@ -2247,4 +2255,3 @@ export type Callback<T> = (
   error: Error | undefined,
   result: T | undefined,
 ) => void
-export type ErrorCallback = (error: Error) => void
diff --git a/lib/utils.ts b/lib/utils.ts
new file mode 100644
index 00000000..a66e5a37
--- /dev/null
+++ b/lib/utils.ts
@@ -0,0 +1,19 @@
+/** Signature for a callback function that expects an error to be passed. */
+export type ErrorCallback = (error: Error, result?: never) => void
+
+/** Unbound `Object.prototype.toString`. */
+const unboundToString = Object.prototype.toString
+
+/** Wrapped `Object.prototype.toString`, so that you don't need to remember to use `.call()`. */
+export const objectToString = (obj: unknown) => unboundToString.call(obj)
+
+/** Safely converts any value to string, using the value's own `toString` when available. */
+export const safeToString = (val: unknown) => {
+  // Ideally, we'd just use String() for everything, but it breaks if `toString` is missing (mostly
+  // values with no prototype), so we have to use Object#toString as a fallback.
+  if (val === undefined || val === null || typeof val.toString === 'function') {
+    return String(val)
+  } else {
+    return objectToString(val)
+  }
+}
diff --git a/lib/validators.ts b/lib/validators.ts
index a99ed49b..35db4755 100644
--- a/lib/validators.ts
+++ b/lib/validators.ts
@@ -25,58 +25,79 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 
 ************************************************************************************ */
-'use strict'
 
-const toString = Object.prototype.toString
+import { ErrorCallback, objectToString, safeToString } from './utils'
 
 /* Validation functions copied from check-types package - https://www.npmjs.com/package/check-types */
-export function isFunction(data: unknown): boolean {
+
+/** Determines whether the argument is a function. */
+export function isFunction(data: unknown): data is Function {
   return typeof data === 'function'
 }
 
+/** Determines whether the argument is a non-empty string. */
 export function isNonEmptyString(data: unknown): boolean {
   return isString(data) && data !== ''
 }
 
+/** Determines whether the argument is a *valid* Date. */
 export function isDate(data: unknown): boolean {
-  if (data instanceof Date) {
-    return isInteger(data.getTime())
-  }
-  return false
+  return isInstanceStrict(data, Date) && isInteger(data.getTime())
 }
 
+/** Determines whether the argument is the empty string. */
 export function isEmptyString(data: unknown): boolean {
   return data === '' || (data instanceof String && data.toString() === '')
 }
 
+/** Determines whether the argument is a string. */
 export function isString(data: unknown): boolean {
   return typeof data === 'string' || data instanceof String
 }
 
+/** Determines whether the string representation of the argument is "[object Object]". */
 export function isObject(data: unknown): boolean {
-  return toString.call(data) === '[object Object]'
+  return objectToString(data) === '[object Object]'
 }
 
+/** Determines whether the first argument is an instance of the second. */
+export function isInstanceStrict<T extends Function>(
+  data: unknown,
+  Constructor: T,
+): data is T['prototype'] {
+  try {
+    return data instanceof Constructor
+  } catch {
+    return false
+  }
+}
+
+/** Determines whether the argument is an integer. */
 export function isInteger(data: unknown): boolean {
   return typeof data === 'number' && data % 1 === 0
 }
-/* End validation functions */
 
-export function validate(bool: boolean, cb?: unknown, options?: unknown): void {
-  if (!isFunction(cb)) {
-    options = cb
-    cb = null
-  }
-  if (!isObject(options)) options = { Error: 'Failed Check' }
-  if (!bool) {
-    if (typeof cb === 'function') {
-      // @ts-ignore
-      cb(new ParameterError(options))
-    } else {
-      // @ts-ignore
-      throw new ParameterError(options)
-    }
-  }
+/* -- End validation functions -- */
+
+/**
+ * When the first argument is false, an error is created with the given message. If a callback is
+ * provided, the error is passed to the callback, otherwise the error is thrown.
+ */
+export function validate(
+  bool: boolean,
+  cbOrMessage?: ErrorCallback | string,
+  message?: string,
+): void {
+  if (bool) return // Validation passes
+  const cb = isFunction(cbOrMessage) ? cbOrMessage : null
+  let options = isFunction(cbOrMessage) ? message : cbOrMessage
+  // The default message prior to v5 was '[object Object]' due to a bug, and the message is kept
+  // for backwards compatibility.
+  if (!isObject(options)) options = '[object Object]'
+
+  const err = new ParameterError(safeToString(options))
+  if (cb) cb(err)
+  else throw err
 }
 
 export class ParameterError extends Error {}
diff --git a/package-lock.json b/package-lock.json
index fc3f5781..167bf701 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -15,6 +15,7 @@
       },
       "devDependencies": {
         "@types/jest": "^29",
+        "@types/node": "^16.18.23",
         "@types/psl": "^1",
         "@types/punycode": "^2",
         "@types/url-parse": "^1.4.8",
@@ -1660,9 +1661,9 @@
       "dev": true
     },
     "node_modules/@types/node": {
-      "version": "18.15.10",
-      "resolved": "https://registry.npmjs.org/@types/node/-/node-18.15.10.tgz",
-      "integrity": "sha512-9avDaQJczATcXgfmMAW3MIWArOO7A+m90vuCFLr8AotWf8igO/mRoYukrk2cqZVtv38tHs33retzHEilM7FpeQ==",
+      "version": "16.18.23",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-16.18.23.tgz",
+      "integrity": "sha512-XAMpaw1s1+6zM+jn2tmw8MyaRDIJfXxqmIQIS0HfoGYPuf7dUWeiUKopwq13KFX9lEp1+THGtlaaYx39Nxr58g==",
       "dev": true
     },
     "node_modules/@types/prettier": {
@@ -7896,9 +7897,9 @@
       "dev": true
     },
     "@types/node": {
-      "version": "18.15.10",
-      "resolved": "https://registry.npmjs.org/@types/node/-/node-18.15.10.tgz",
-      "integrity": "sha512-9avDaQJczATcXgfmMAW3MIWArOO7A+m90vuCFLr8AotWf8igO/mRoYukrk2cqZVtv38tHs33retzHEilM7FpeQ==",
+      "version": "16.18.23",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-16.18.23.tgz",
+      "integrity": "sha512-XAMpaw1s1+6zM+jn2tmw8MyaRDIJfXxqmIQIS0HfoGYPuf7dUWeiUKopwq13KFX9lEp1+THGtlaaYx39Nxr58g==",
       "dev": true
     },
     "@types/prettier": {
diff --git a/package.json b/package.json
index 8d3ffa67..85d0e571 100644
--- a/package.json
+++ b/package.json
@@ -100,13 +100,14 @@
   },
   "devDependencies": {
     "@types/jest": "^29",
+    "@types/node": "^16.18.23",
     "@types/psl": "^1",
     "@types/punycode": "^2",
     "@types/url-parse": "^1.4.8",
+    "@typescript-eslint/eslint-plugin": "^5.57.0",
+    "@typescript-eslint/parser": "^5.57.0",
     "async": "2.6.4",
     "eslint": "^8.36.0",
-    "@typescript-eslint/parser": "^5.57.0",
-    "@typescript-eslint/eslint-plugin": "^5.57.0",
     "eslint-config-prettier": "^8.8.0",
     "eslint-plugin-prettier": "^4.2.1",
     "genversion": "^3.1.1",