diff --git a/README.md b/README.md
index 59a99d9fd..f7c299cf5 100644
--- a/README.md
+++ b/README.md
@@ -70,6 +70,24 @@ JWT::$leeway = 60; // $leeway in seconds
 $decoded = JWT::decode($jwt, new Key($key, 'HS256'));
 ```
 
+### Millisecond timestamps
+
+RFC 7519 requires the `iat`, `nbf` and `exp` claims to be expressed in
+**seconds** since the Unix epoch. Some non-compliant token issuers emit these
+claims in **milliseconds** instead, which causes `decode` to reject the token
+(for example, throwing `Cannot handle token with iat prior to ...` with a date
+far in the future).
+
+If you must consume such tokens, opt in by enabling millisecond mode. When
+enabled, the reference time defaults to milliseconds
+(`microtime(true) * 1000`), so claims are compared in the same unit. If you also
+set `JWT::$timestamp` or `JWT::$leeway`, express them in milliseconds too.
+
+```php
+JWT::$useMillisecondTimestamps = true;
+$decoded = JWT::decode($jwt, new Key($key, 'HS256'));
+```
+
 ## Example encode/decode headers
 
 Decoding the JWT headers without verifying the JWT first is NOT recommended, and is not supported by
diff --git a/src/ExpiredException.php b/src/ExpiredException.php
index 25f445132..5371fd5d3 100644
--- a/src/ExpiredException.php
+++ b/src/ExpiredException.php
@@ -6,7 +6,7 @@ class ExpiredException extends \UnexpectedValueException implements JWTException
 {
     private object $payload;
 
-    private ?int $timestamp = null;
+    private int|float|null $timestamp = null;
 
     public function setPayload(object $payload): void
     {
@@ -18,12 +18,16 @@ public function getPayload(): object
         return $this->payload;
     }
 
-    public function setTimestamp(int $timestamp): void
+    /**
+     * @param int|float $timestamp Seconds, or milliseconds when
+     *                             JWT::$useMillisecondTimestamps is enabled.
+     */
+    public function setTimestamp(int|float $timestamp): void
     {
         $this->timestamp = $timestamp;
     }
 
-    public function getTimestamp(): ?int
+    public function getTimestamp(): int|float|null
     {
         return $this->timestamp;
     }
diff --git a/src/JWT.php b/src/JWT.php
index 1c71ab3d0..df3d1f1aa 100644
--- a/src/JWT.php
+++ b/src/JWT.php
@@ -38,19 +38,47 @@ class JWT
      * we want to provide some extra leeway time to
      * account for clock skew.
      *
+     * When `JWT::$useMillisecondTimestamps` is enabled, this must be
+     * expressed in milliseconds.
+     *
+     * @var int
+    /**
+     * When checking nbf, iat or expiration times,
+     * we want to provide some extra leeway time to
+     * account for clock skew.
+     * 
+     * NOTE: When `JWT::$useMillisecondTimestamps` is enabled, 
+     * this must be expressed in milliseconds.
+     *
      * @var int
      */
     public static $leeway = 0;
+    public static $leeway = 0;
 
     /**
      * Allow the current timestamp to be specified.
      * Useful for fixing a value within unit testing.
      * Will default to PHP time() value if null.
      *
-     * @var ?int
+     * @var int|float|null
      */
     public static $timestamp = null;
 
+    /**
+     * When true, the 'iat', 'nbf' and 'exp' claims are interpreted as
+     * millisecond timestamps rather than the seconds mandated by RFC 7519.
+     *
+     * Some non-compliant token issuers emit these claims in milliseconds.
+     * Enabling this makes the reference time default to milliseconds
+     * (microtime(true) * 1000) so claims are compared in the same unit.
+     *
+     * NOTE: When enabled, `JWT::$timestamp` and `JWT::$leeway` must also be
+     * expressed in milliseconds if you set them.
+     *
+     * @var bool
+     */
+    public static $useMillisecondTimestamps = false;
+
     /**
      * @var array<string, string[]>
      */
@@ -102,7 +130,15 @@ public static function decode(
         ?stdClass &$headers = null
     ): stdClass {
         // Validate JWT
-        $timestamp = \is_null(static::$timestamp) ? \time() : static::$timestamp;
+        if (!\is_null(static::$timestamp)) {
+            $timestamp = static::$timestamp;
+        } elseif (static::$useMillisecondTimestamps) {
+            // Keep the value as a float to avoid integer overflow on 32-bit
+            // systems, where a millisecond timestamp exceeds PHP_INT_MAX.
+            $timestamp = \round(\microtime(true) * 1000);
+        } else {
+            $timestamp = \time();
+        }
 
         if (empty($keyOrKeyArray)) {
             throw new InvalidArgumentException('Key may not be empty');
@@ -167,7 +203,7 @@ public static function decode(
         // token can actually be used. If it's not yet that time, abort.
         if (isset($payload->nbf) && floor($payload->nbf) > ($timestamp + static::$leeway)) {
             $ex = new BeforeValidException(
-                'Cannot handle token with nbf prior to ' . \date(DateTime::ATOM, (int) floor($payload->nbf))
+                'Cannot handle token with nbf prior to ' . \date(DateTime::ATOM, self::claimToSeconds($payload->nbf))
             );
             $ex->setPayload($payload);
             throw $ex;
@@ -178,7 +214,7 @@ public static function decode(
         // correctly used the nbf claim).
         if (!isset($payload->nbf) && isset($payload->iat) && floor($payload->iat) > ($timestamp + static::$leeway)) {
             $ex = new BeforeValidException(
-                'Cannot handle token with iat prior to ' . \date(DateTime::ATOM, (int) floor($payload->iat))
+                'Cannot handle token with iat prior to ' . \date(DateTime::ATOM, self::claimToSeconds($payload->iat))
             );
             $ex->setPayload($payload);
             throw $ex;
@@ -546,6 +582,24 @@ private static function handleJsonError(int $errno): void
         );
     }
 
+    /**
+     * Convert a date claim to whole seconds for human-readable output,
+     * accounting for `JWT::$useMillisecondTimestamps`.
+     *
+     * @param int|float|string $claim The 'iat', 'nbf' or 'exp' claim value.
+     *
+     * @return int Unix timestamp in seconds.
+     */
+    private static function claimToSeconds($claim): int
+    {
+        $seconds = (float) $claim;
+        if (static::$useMillisecondTimestamps) {
+            $seconds /= 1000;
+        }
+
+        return (int) \floor($seconds);
+    }
+
     /**
      * Get the number of bytes in cryptographic strings.
      *
diff --git a/tests/JWTTest.php b/tests/JWTTest.php
index 40f45149c..09a246913 100644
--- a/tests/JWTTest.php
+++ b/tests/JWTTest.php
@@ -310,6 +310,111 @@ public function testInvalidTokenWithIatMicrotime()
         JWT::decode($encoded, $this->hmacKey);
     }
 
+    /**
+     * @runInSeparateProcess
+     */
+    public function testValidTokenWithMillisecondTimestamps()
+    {
+        JWT::$useMillisecondTimestamps = true;
+        $nowMs = round(microtime(true) * 1000);
+        $payload = [
+            'message' => 'abc',
+            'iat' => $nowMs,
+            'exp' => $nowMs + 20000, // 20s in the future, in ms
+        ];
+        $encoded = JWT::encode($payload, $this->hmacKey->getKeyMaterial(), 'HS256');
+        $decoded = JWT::decode($encoded, $this->hmacKey);
+        $this->assertSame('abc', $decoded->message);
+    }
+
+    /**
+     * @runInSeparateProcess
+     */
+    public function testValidTokenWithMillisecondTimestampsAndExplicitOverrides()
+    {
+        JWT::$useMillisecondTimestamps = true;
+        // Fix "now" to a value that exceeds 32-bit PHP_INT_MAX, expressed in ms.
+        JWT::$timestamp = 1710000000000; // 2024-03-09T16:00:00Z in ms
+        JWT::$leeway = 60000; // 60s of leeway, in ms
+        $payload = [
+            'message' => 'abc',
+            // exp is 30s in the past, but within the 60s (ms) leeway window.
+            'exp' => JWT::$timestamp - 30000,
+            // nbf is 30s in the future, also within the leeway window.
+            'nbf' => JWT::$timestamp + 30000,
+        ];
+        $encoded = JWT::encode($payload, $this->hmacKey->getKeyMaterial(), 'HS256');
+        $decoded = JWT::decode($encoded, $this->hmacKey);
+        $this->assertSame('abc', $decoded->message);
+    }
+
+    /**
+     * @runInSeparateProcess
+     */
+    public function testMillisecondIatIsRejectedWithoutFlag()
+    {
+        $this->expectException(BeforeValidException::class);
+        $this->expectExceptionMessage('Cannot handle token with iat prior to');
+        $payload = [
+            'message' => 'abc',
+            'iat' => round(microtime(true) * 1000), // ms timestamp, but flag disabled
+        ];
+        $encoded = JWT::encode($payload, $this->hmacKey->getKeyMaterial(), 'HS256');
+        JWT::decode($encoded, $this->hmacKey);
+    }
+
+    /**
+     * @runInSeparateProcess
+     */
+    public function testExpiredTokenWithMillisecondTimestamps()
+    {
+        $this->expectException(ExpiredException::class);
+        JWT::$useMillisecondTimestamps = true;
+        $payload = [
+            'message' => 'abc',
+            'exp' => round(microtime(true) * 1000) - 20000, // 20s in the past, in ms
+        ];
+        $encoded = JWT::encode($payload, $this->hmacKey->getKeyMaterial(), 'HS256');
+        JWT::decode($encoded, $this->hmacKey);
+    }
+
+    /**
+     * @runInSeparateProcess
+     */
+    public function testBeforeValidTokenWithMillisecondNbf()
+    {
+        $this->expectException(BeforeValidException::class);
+        $this->expectExceptionMessage('Cannot handle token with nbf prior to');
+        JWT::$useMillisecondTimestamps = true;
+        $payload = [
+            'message' => 'abc',
+            'nbf' => round(microtime(true) * 1000) + 20000, // 20s in the future, in ms
+        ];
+        $encoded = JWT::encode($payload, $this->hmacKey->getKeyMaterial(), 'HS256');
+        JWT::decode($encoded, $this->hmacKey);
+    }
+
+    /**
+     * @runInSeparateProcess
+     */
+    public function testMillisecondExceptionMessageRendersCorrectDate()
+    {
+        JWT::$useMillisecondTimestamps = true;
+        // 2033-05-18T03:33:20+00:00 expressed in milliseconds
+        $iatMs = 2000000000 * 1000;
+        $payload = [
+            'message' => 'abc',
+            'iat' => $iatMs,
+        ];
+        $encoded = JWT::encode($payload, $this->hmacKey->getKeyMaterial(), 'HS256');
+        try {
+            JWT::decode($encoded, $this->hmacKey);
+            $this->fail('Expected BeforeValidException was not thrown');
+        } catch (BeforeValidException $e) {
+            $this->assertStringContainsString('2033-05-18T03:33:20+00:00', $e->getMessage());
+        }
+    }
+
     public function testInvalidToken()
     {
         $encodeKey = $this->generateHmac256();