diff --git a/system/core/Input.php b/system/core/Input.php
index 12332cf..b0bbb7b 100644
--- a/system/core/Input.php
+++ b/system/core/Input.php
@@ -799,19 +799,27 @@
 	 */
 	public function get_request_header($index, $xss_clean = FALSE)
 	{
-		if (empty($this->headers))
+		static $headers;
+
+		if ( ! isset($headers))
 		{
-			$this->request_headers();
+			empty($this->headers) OR $this->request_headers();
+			foreach ($this->headers as $key => $value)
+			{
+				$headers[strtolower($key)] = $value;
+			}
 		}
 
-		if ( ! isset($this->headers[$index]))
+		$index = strtolower($index);
+
+		if ( ! isset($headers[$index]))
 		{
 			return NULL;
 		}
 
 		return ($xss_clean === TRUE)
-			? $this->security->xss_clean($this->headers[$index])
-			: $this->headers[$index];
+			? $this->security->xss_clean($headers[$index])
+			: $headers[$index];
 	}
 
 	// --------------------------------------------------------------------
diff --git a/user_guide_src/source/changelog.rst b/user_guide_src/source/changelog.rst
index 5c2c4d9..7e14152 100644
--- a/user_guide_src/source/changelog.rst
+++ b/user_guide_src/source/changelog.rst
@@ -30,6 +30,7 @@
 -  Fixed a bug (#3846) - :doc:`Image Manipulation Library <libraries/image_lib>` method `image_mirror_gd()` didn't properly initialize its variables.
 -  Fixed a bug (#3854) - `field_data()` didn't work properly with the Oracle (OCI8) database driver.
 -  Fixed a bug in the :doc:`Database Utility Class <database/utilities>` method ``csv_from_result()`` didn't work with a whitespace CSV delimiter.
+-  Fixed a bug (#3890) - :doc:`Input Library <libraries/input>` method ``get_request_header()`` treated header names as case-sensitive.
 
 Version 3.0.0
 =============