diff --git a/administrator/components/com_admin/script.php b/administrator/components/com_admin/script.php
index db7b1840996d5..12601eb970dd0 100644
--- a/administrator/components/com_admin/script.php
+++ b/administrator/components/com_admin/script.php
@@ -1519,7 +1519,6 @@ public function deleteUnexistingFiles()
 			'/media/editors/tinymce/skins/lightgray/fonts/tinymce.dev.svg',
 			'/media/editors/tinymce/skins/lightgray/img/wline.gif',
 			'/media/mod_languages/images/km_kr.gif',
-			'/media/mod_languages/images/si_LK.gif',
 			'/plugins/editors/codemirror/styles.css',
 			'/plugins/editors/codemirror/styles.min.css',
 
@@ -1539,7 +1538,6 @@ public function deleteUnexistingFiles()
 			'/libraries/simplepie/idn/idna_convert.class.php',
 			'/libraries/simplepie/idn/npdata.ser',
 			'/libraries/simplepie/simplepie.php',
-			'/media/mod_languages/images/si_lk.gif',
 			'/media/system/js/permissions.min.js',
 			'/plugins/editors/tinymce/fields/skins.php',
 			'/plugins/user/profile/fields/dob.php',
@@ -2324,6 +2322,8 @@ public function deleteUnexistingFiles()
 		{
 			JFile::delete(JPATH_ROOT . '/administrator/manifests/packages/pkg_weblinks.xml');
 		}
+
+		$this->fixFilenameCasing();
 	}
 
 	/**
@@ -2657,4 +2657,67 @@ private function cleanJoomlaCache()
 		$model->setState('client_id', 1);
 		$model->clean();
 	}
+
+	/**
+	 * Renames or removes incorrectly cased files.
+	 *
+	 * @return  void
+	 *
+	 * @since   __DEPLOY_VERSION__
+	 */
+	protected function fixFilenameCasing()
+	{
+		$files = array(
+			'libraries/src/Filesystem/Support/Stringcontroller.php' => 'libraries/src/Filesystem/Support/StringController.php',
+			'libraries/vendor/paragonie/sodium_compat/src/Core/Xsalsa20.php' => 'libraries/vendor/paragonie/sodium_compat/src/Core/XSalsa20.php',
+			'media/mod_languages/images/si_LK.gif' => 'media/mod_languages/images/si_lk.gif',
+		);
+
+		foreach ($files as $old => $expected)
+		{
+			$oldRealpath = realpath(JPATH_ROOT . '/' . $old);
+
+			// On Unix without incorrectly cased file.
+			if ($oldRealpath === false)
+			{
+				continue;
+			}
+
+			$oldBasename      = basename($oldRealpath);
+			$newRealpath      = realpath(JPATH_ROOT . '/' . $expected);
+			$newBasename      = basename($newRealpath);
+			$expectedBasename = basename($expected);
+
+			// On Windows or Unix with only the incorrectly cased file.
+			if ($newBasename !== $expectedBasename)
+			{
+				// Rename the file.
+				rename(JPATH_ROOT . '/' . $old, JPATH_ROOT . '/' . $old . '.tmp');
+				rename(JPATH_ROOT . '/' . $old . '.tmp', JPATH_ROOT . '/' . $expected);
+
+				continue;
+			}
+
+			// There might still be an incorrectly cased file on other OS than Windows.
+			if ($oldBasename === basename($old))
+			{
+				// Check if case-insensitive file system, eg on OSX.
+				if (fileinode($oldRealpath) === fileinode($newRealpath))
+				{
+					// Check deeper because even realpath or glob might not return the actual case.
+					if (!in_array($expectedBasename, scandir(dirname($newRealpath))))
+					{
+						// Rename the file.
+						rename(JPATH_ROOT . '/' . $old, JPATH_ROOT . '/' . $old . '.tmp');
+						rename(JPATH_ROOT . '/' . $old . '.tmp', JPATH_ROOT . '/' . $expected);
+					}
+				}
+				else
+				{
+					// On Unix with both files: Delete the incorrectly cased file.
+					unlink(JPATH_ROOT . '/' . $old);
+				}
+			}
+		}
+	}
 }
diff --git a/libraries/src/Filesystem/Streams/StreamString.php b/libraries/src/Filesystem/Streams/StreamString.php
index 167447fbfab18..f48006c5a3ab8 100644
--- a/libraries/src/Filesystem/Streams/StreamString.php
+++ b/libraries/src/Filesystem/Streams/StreamString.php
@@ -10,7 +10,7 @@
 
 defined('JPATH_PLATFORM') or die;
 
-use Joomla\CMS\Filesystem\Support\Stringcontroller;
+use Joomla\CMS\Filesystem\Support\StringController;
 
 /**
  * String Stream Wrapper
diff --git a/libraries/src/Filesystem/Support/Stringcontroller.php b/libraries/src/Filesystem/Support/StringController.php
similarity index 100%
rename from libraries/src/Filesystem/Support/Stringcontroller.php
rename to libraries/src/Filesystem/Support/StringController.php
diff --git a/libraries/vendor/paragonie/sodium_compat/src/Core/Xsalsa20.php b/libraries/vendor/paragonie/sodium_compat/src/Core/XSalsa20.php
similarity index 100%
rename from libraries/vendor/paragonie/sodium_compat/src/Core/Xsalsa20.php
rename to libraries/vendor/paragonie/sodium_compat/src/Core/XSalsa20.php