diff --git a/src/Debug/EmailCollector.php b/src/Debug/EmailCollector.php
index df2601a..3a0a9dd 100644
--- a/src/Debug/EmailCollector.php
+++ b/src/Debug/EmailCollector.php
@@ -12,6 +12,7 @@
 use Framework\Debug\Collector;
 use Framework\Debug\Debugger;
 use Framework\Email\Header;
+use Framework\Email\Mailer;
 
 /**
  * Class EmailCollector.
@@ -20,6 +21,14 @@
  */
 class EmailCollector extends Collector
 {
+    protected Mailer $mailer;
+
+    public function setMailer(Mailer $mailer) : static
+    {
+        $this->mailer = $mailer;
+        return $this;
+    }
+
     public function getActivities() : array
     {
         $activities = [];
@@ -38,6 +47,10 @@ public function getActivities() : array
     public function getContents() : string
     {
         \ob_start();
+        if ( ! isset($this->mailer)) {
+            echo '<p>This collector has not been added to a Mailer instance.</p>';
+            return \ob_get_clean(); // @phpstan-ignore-line
+        }
         if ( ! $this->hasData()) {
             echo '<p>No messages have been sent.</p>';
             return \ob_get_clean(); // @phpstan-ignore-line
diff --git a/src/Mailer.php b/src/Mailer.php
index c1365bd..b215da0 100644
--- a/src/Mailer.php
+++ b/src/Mailer.php
@@ -178,6 +178,7 @@ abstract public function send(Message $message) : bool;
 
     public function setDebugCollector(EmailCollector $collector) : static
     {
+        $collector->setMailer($this);
         $this->debugCollector = $collector;
         return $this;
     }
diff --git a/tests/Debug/EmailCollectorTest.php b/tests/Debug/EmailCollectorTest.php
index 262dfd4..e09e8d5 100644
--- a/tests/Debug/EmailCollectorTest.php
+++ b/tests/Debug/EmailCollectorTest.php
@@ -35,8 +35,17 @@ protected function makeMailer() : Mailer
         return $mailer;
     }
 
+    public function testNoMailer() : void
+    {
+        self::assertStringContainsString(
+            'This collector has not been added to a Mailer instance',
+            $this->collector->getContents()
+        );
+    }
+
     public function testNoData() : void
     {
+        $this->makeMailer();
         self::assertStringContainsString(
             'No messages have been sent',
             $this->collector->getContents()