diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/RemoteEvent/MailgunPayloadConverter.php b/src/Symfony/Component/Mailer/Bridge/Mailgun/RemoteEvent/MailgunPayloadConverter.php
index 7f1e52477d8ff..cb3f323861030 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/RemoteEvent/MailgunPayloadConverter.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/RemoteEvent/MailgunPayloadConverter.php
@@ -50,8 +50,8 @@ public function convert(array $payload): AbstractMailerEvent
             };
             $event = new MailerEngagementEvent($name, $payload['id'], $payload);
         }
-        if (!$date = \DateTimeImmutable::createFromFormat('U.u', $payload['timestamp'])) {
-            throw new ParseException(sprintf('Invalid date "%s".', $payload['timestamp']));
+        if (!$date = \DateTimeImmutable::createFromFormat('U.u', sprintf('%.6F', $payload['timestamp']))) {
+            throw new ParseException(sprintf('Invalid date "%s".', sprintf('%.6F', $payload['timestamp'])));
         }
         $event->setDate($date);
         $event->setRecipientEmail($payload['recipient']);
diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/clicks.php b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/clicks.php
index cd556e6d26168..9aac4c899d6b9 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/clicks.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/clicks.php
@@ -6,6 +6,6 @@
 $wh->setRecipientEmail('alice@example.com');
 $wh->setTags(['my_tag_1', 'my_tag_2']);
 $wh->setMetadata(['my_var_1' => 'Mailgun Variable #1', 'my-var-2' => 'awesome']);
-$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', 1521243339.873676));
+$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', '1521243339.873676'));
 
 return $wh;
diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/delivered_messages.json b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/delivered_messages.json
index 1b0e4046b3ded..58700a5eb3c64 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/delivered_messages.json
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/delivered_messages.json
@@ -6,7 +6,7 @@
     },
     "event-data": {
         "id": "CPgfbmQMTCKtHW6uIWtuVe",
-        "timestamp": 1521472262.908181,
+        "timestamp": 1521472262.000002,
         "log-level": "info",
         "event": "delivered",
         "delivery-status": {
diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/delivered_messages.php b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/delivered_messages.php
index 7240b90a96ef2..efb215d5f9fab 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/delivered_messages.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/delivered_messages.php
@@ -6,7 +6,7 @@
 $wh->setRecipientEmail('alice@example.com');
 $wh->setTags(['my_tag_1', 'my_tag_2']);
 $wh->setMetadata(['my_var_1' => 'Mailgun Variable #1', 'my-var-2' => 'awesome']);
-$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', 1521472262.908181));
+$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', '1521472262.000002'));
 $wh->setReason('OK');
 
 return $wh;
diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/opens.php b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/opens.php
index f224ca13bd78c..da8132ae3d747 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/opens.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/opens.php
@@ -6,6 +6,6 @@
 $wh->setRecipientEmail('alice@example.com');
 $wh->setTags(['my_tag_1', 'my_tag_2']);
 $wh->setMetadata(['my_var_1' => 'Mailgun Variable #1', 'my-var-2' => 'awesome']);
-$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', 1521243339.873676));
+$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', '1521243339.873676'));
 
 return $wh;
diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/permanent_failure.php b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/permanent_failure.php
index 51798f3ce77b7..8dfffd0362e85 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/permanent_failure.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/permanent_failure.php
@@ -6,7 +6,7 @@
 $wh->setRecipientEmail('alice@example.com');
 $wh->setTags(['my_tag_1', 'my_tag_2']);
 $wh->setMetadata(['my_var_1' => 'Mailgun Variable #1', 'my-var-2' => 'awesome']);
-$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', 1521233195.375624));
+$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', '1521233195.375624'));
 $wh->setReason('No Such User Here');
 
 return $wh;
diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/spam_complaints.php b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/spam_complaints.php
index 224a79dc3fb41..4695a876849e9 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/spam_complaints.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/spam_complaints.php
@@ -6,6 +6,6 @@
 $wh->setRecipientEmail('alice@example.com');
 $wh->setTags(['my_tag_1', 'my_tag_2']);
 $wh->setMetadata(['my_var_1' => 'Mailgun Variable #1', 'my-var-2' => 'awesome']);
-$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', 1521233123.501324));
+$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', '1521233123.501324'));
 
 return $wh;
diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/suppression_failure.php b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/suppression_failure.php
index f5bb1a4d0c407..e24946dae9bd7 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/suppression_failure.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/suppression_failure.php
@@ -6,7 +6,7 @@
 $wh->setRecipientEmail('alice@example.com');
 $wh->setTags(['my_tag_1', 'my_tag_2']);
 $wh->setMetadata(['my_var_1' => 'Mailgun Variable #1', 'my-var-2' => 'awesome']);
-$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', 1521233195.375624));
+$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', '1521233195.375624'));
 $wh->setReason('Not delivering to previously bounced address');
 
 return $wh;
diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/temporary_failure.php b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/temporary_failure.php
index 0ca8a48bc9e10..8f969745ba155 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/temporary_failure.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/temporary_failure.php
@@ -6,7 +6,7 @@
 $wh->setRecipientEmail('alice@example.com');
 $wh->setTags(['my_tag_1', 'my_tag_2']);
 $wh->setMetadata(['my_var_1' => 'Mailgun Variable #1', 'my-var-2' => 'awesome']);
-$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', 1521472262.908181));
+$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', '1521472262.908181'));
 $wh->setReason("4.2.2 The email account that you tried to reach is over quota. Please direct\n4.2.2 the recipient to\n4.2.2  https://support.example.com/mail/?p=422");
 
 return $wh;
diff --git a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/unsubscribes.php b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/unsubscribes.php
index 1f38f2e9184ff..7261cbbc0e9b6 100644
--- a/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/unsubscribes.php
+++ b/src/Symfony/Component/Mailer/Bridge/Mailgun/Tests/Webhook/Fixtures/unsubscribes.php
@@ -6,6 +6,6 @@
 $wh->setRecipientEmail('alice@example.com');
 $wh->setTags(['my_tag_1', 'my_tag_2']);
 $wh->setMetadata(['my_var_1' => 'Mailgun Variable #1', 'my-var-2' => 'awesome']);
-$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', 1521243339.873676));
+$wh->setDate(\DateTimeImmutable::createFromFormat('U.u', '1521243339.873676'));
 
 return $wh;