diff --git a/examples/progress.php b/examples/progress.php
index 8e37512..0d0efec 100644
--- a/examples/progress.php
+++ b/examples/progress.php
@@ -1,6 +1,8 @@
 <?php
 require __DIR__ . '/../vendor/autoload.php';
 
+// Note: The server needs to send a content-length header for progress to work.
+
 use \Curl\Curl;
 
 $curl = new Curl();
diff --git a/examples/progress_advanced.php b/examples/progress_advanced.php
index c1b0388..fe64629 100644
--- a/examples/progress_advanced.php
+++ b/examples/progress_advanced.php
@@ -1,6 +1,8 @@
 <?php
 require __DIR__ . '/../vendor/autoload.php';
 
+// Note: The server needs to send a content-length header for progress to work.
+
 use \Curl\Curl;
 
 $curl = new Curl();