diff --git a/README.md b/README.md
index c370c59..3a8489c 100644
--- a/README.md
+++ b/README.md
@@ -27,13 +27,15 @@ $event = NowCal::create(['start' => 'October 5, 2019 6:03PM']))
 
 The following properties can be get/set on the NowCal instance. Users can take advantage of the set property helpers in the class, i.e.: `$nowcal->location('Event Location');` as they provide a nice syntax to string multiple calls together and support callbacks if necessary.
 
-| Property | Description                                                                                            |
-| -------- | ------------------------------------------------------------------------------------------------------ |
-| start    | A string parseable by DateTime                                                                         |
-| end      | A string parseable by DateTime, as per RFC 5545, only an end value or duration value may be used       |
-| duration | A string parseable by DateInterval, as per RFC 5545, only an end value or duration value may be used   |
-| summary  | A short description of the event                                                                       |
-| location | The location where the event is taking place                                                           |
+| Property | Description                                                                                                                         |
+| -------- | ----------------------------------------------------------------------------------------------------------------------------------- |
+| uid      | A globally unique ID. NOTE: passing the same ICS file into a calendar app with the same UI allows you to update the existing invite |
+| start    | A string parseable by DateTime                                                                                                      |
+| timezone | A string parseable by DateTimeZone                                                                                                  |
+| end      | A string parseable by DateTime, as per RFC 5545, only an end value or duration value may be used                                    |
+| duration | A string parseable by DateInterval, as per RFC 5545, only an end value or duration value may be used                                |
+| summary  | A short description of the event                                                                                                    |
+| location | The location where the event is taking place                                                                                        |
 
 ### Methods
 
diff --git a/src/NowCal/NowCal.php b/src/NowCal/NowCal.php
index 22dae3e..88baa23 100644
--- a/src/NowCal/NowCal.php
+++ b/src/NowCal/NowCal.php
@@ -2,9 +2,11 @@
 
 namespace NowCal;
 
+use Closure;
 use DateInterval;
 use DateTime;
 use DateTimeZone;
+use Exception;
 
 class NowCal
 {
@@ -37,6 +39,7 @@ class NowCal
      * @see https://tools.ietf.org/html/rfc5545#section-3.8
      */
     public const ALLOWED = [
+        'uid',
         'end',
         'start',
         'summary',
@@ -102,6 +105,14 @@ class NowCal
      */
     protected string $version = '2.0';
 
+    /**
+     * The globally unique identifier for the calendar component. If not
+     * provided one will be generated automatically.
+     *
+     * @see https://datatracker.ietf.org/doc/html/rfc5545#section-3.8.4.7
+     */
+    public ?string $uid = null;
+
     /**
      * This property specifies when the calendar component begins.
      *
@@ -203,10 +214,17 @@ public static function file(array $props = []): string
         return self::create($props)->file;
     }
 
+    public function uid(string|Closure $uid): self
+    {
+        $this->set('uid', $uid);
+
+        return $this;
+    }
+
     /**
      * Set the event's start date.
      */
-    public function start(string|\Closure|\DateTime $datetime): self
+    public function start(string|Closure|DateTime $datetime): self
     {
         $this->set('start', $datetime);
 
@@ -216,7 +234,7 @@ public function start(string|\Closure|\DateTime $datetime): self
     /**
      * Set the event's end date.
      */
-    public function end(string|\Closure|\DateTime $datetime): self
+    public function end(string|Closure|DateTime $datetime): self
     {
         if (!$this->has('duration')) {
             $this->set('end', $datetime);
@@ -228,7 +246,7 @@ public function end(string|\Closure|\DateTime $datetime): self
     /**
      * Set the event's summary.
      */
-    public function summary(string|\Closure $summary): self
+    public function summary(string|Closure $summary): self
     {
         $this->set('summary', $summary);
 
@@ -238,7 +256,7 @@ public function summary(string|\Closure $summary): self
     /**
      * Set the event's location.
      */
-    public function location(string|\Closure $location): self
+    public function location(string|Closure $location): self
     {
         $this->set('location', $location);
 
@@ -248,7 +266,7 @@ public function location(string|\Closure $location): self
     /**
      * Set the event's duration using a DateInterval.
      */
-    public function duration(string|\Closure $duration): self
+    public function duration(string|Closure $duration): self
     {
         if (!$this->has('end')) {
             $this->set('duration', $duration);
@@ -260,7 +278,7 @@ public function duration(string|\Closure $duration): self
     /**
      * Set the event's duration using a DateInterval.
      */
-    public function timezone(string|\Closure $timezone): self
+    public function timezone(string|DateTimeZone|Closure $timezone): self
     {
         $this->set('timezone', $timezone);
 
@@ -430,14 +448,13 @@ protected function createTimezone(): void
             }
 
             if (!$hasDaylightSavings && $transition['isdst']) {
+                $daylight = $transition;
                 $hasDaylightSavings = true;
-            }
 
-            if ($transition['isdst']) {
-                $daylight = $transition;
-            } else {
-                $standard = $transition;
+                continue;
             }
+
+            $standard = $transition;
         }
 
         $this->output[] = 'BEGIN:STANDARD';
@@ -493,7 +510,7 @@ protected function getParameter(string $key): string
         }
 
         if ($this->required($key)) {
-            throw new \Exception('Key "' . $key . '" is not set but is required');
+            throw new Exception('Key "' . $key . '" is not set but is required');
         }
     }
 
@@ -563,6 +580,10 @@ protected function getEventParametersAttribute(): array
      */
     protected function getUidAttribute(): string
     {
+        if ($this->uid) {
+            return $this->uid;
+        }
+
         // Generate 16 bytes (128 bits) of random data or use the data passed into the function.
         $data = $data ?? random_bytes(16);
         assert(strlen($data) == 16);
@@ -645,7 +666,7 @@ protected function convertStringToPascalCase(string $string): string
     /**
      * Parses and creates a datetime.
      */
-    protected function createDateTime(string|DateTime|\Closure $datetime = 'now'): string
+    protected function createDateTime(string|DateTime|Closure $datetime = 'now'): string
     {
         return (new DateTime($datetime ?? 'now'))
             ->format(static::DATETIME_FORMAT);
diff --git a/tests/NowCal/NowCalTest.php b/tests/NowCal/NowCalTest.php
index 15db16d..0b9adb7 100644
--- a/tests/NowCal/NowCalTest.php
+++ b/tests/NowCal/NowCalTest.php
@@ -134,4 +134,11 @@ public function test_places_that_do_not_witness_dst_dont_get_daylight_hours()
 
         echo $this->nowcal->plain;
     }
+
+    public function test_it_can_customize_the_uid()
+    {
+        $this->nowcal->uid($uid = 'abcd-1234');
+
+        $this->assertEquals($uid, $this->nowcal->uid);
+    }
 }