diff --git a/phpBB/includes/acp/acp_board.php b/phpBB/includes/acp/acp_board.php
index 8e571de379..968c9762cc 100644
--- a/phpBB/includes/acp/acp_board.php
+++ b/phpBB/includes/acp/acp_board.php
@@ -510,6 +510,29 @@ class acp_board
 			}
 		}
 
+		if ($mode == 'avatar' && $cfg_array['allow_avatar_upload'])
+		{
+			// If avatar uploading is enabled but the path setting is empty,
+			// config variable validation is bypassed. Catch the case here
+			if (!$cfg_array['avatar_path'])
+			{
+				$error[] = $language->lang('AVATAR_NO_UPLOAD_PATH');
+			}
+			else if (!$submit)
+			{
+				$filesystem = $phpbb_container->get('filesystem');
+				$avatar_path_exists = $filesystem->exists($phpbb_root_path . $cfg_array['avatar_path']);
+				$avatar_path_writable = $filesystem->is_writable($phpbb_root_path . $cfg_array['avatar_path']);
+
+				// Not existing or writable path will be caught on submit by validate_config_vars().
+				// Display the warning if the directory was changed on the server afterwards
+				if (!$avatar_path_exists || !$avatar_path_writable)
+				{
+					$error[] = $language->lang('AVATAR_NO_UPLOAD_DIR');
+				}
+			}
+		}
+
 		// We validate the complete config if wished
 		validate_config_vars($display_vars['vars'], $cfg_array, $error);
 
diff --git a/phpBB/language/en/common.php b/phpBB/language/en/common.php
index 3f8117b7af..fefb7dafb6 100644
--- a/phpBB/language/en/common.php
+++ b/phpBB/language/en/common.php
@@ -110,6 +110,8 @@ $lang = array_merge($lang, array(
 	'AVATAR_NOT_UPLOADED'			=> 'Avatar could not be uploaded.',
 	'AVATAR_NO_TEMP_DIR'			=> 'Temporary folder could not be found or is not writable.',
 	'AVATAR_NO_SIZE'				=> 'The width or height of the linked avatar could not be determined. Please enter them manually.',
+	'AVATAR_NO_UPLOAD_DIR'			=> 'Avatar storage path does not exist or is not writable.',
+	'AVATAR_NO_UPLOAD_PATH'			=> 'Avatar uploading is enabled but avatar storage path is not set.',
 	'AVATAR_PARTIAL_UPLOAD'			=> 'The specified file was only partially uploaded.',
 	'AVATAR_PHP_SIZE_NA'			=> 'The avatar’s filesize is too large.<br />The maximum allowed filesize set in php.ini could not be determined.',
 	'AVATAR_PHP_SIZE_OVERRUN'		=> 'The avatar’s filesize is too large. The maximum allowed upload size is %1$d %2$s.<br />Please note this is set in php.ini and cannot be overridden.',
diff --git a/tests/functional/acp_avatar_settings_test.php b/tests/functional/acp_avatar_settings_test.php
new file mode 100644
index 0000000000..254459ad33
--- /dev/null
+++ b/tests/functional/acp_avatar_settings_test.php
@@ -0,0 +1,83 @@
+<?php
+/**
+*
+* This file is part of the phpBB Forum Software package.
+*
+* @copyright (c) phpBB Limited <https://www.phpbb.com>
+* @license GNU General Public License, version 2 (GPL-2.0)
+*
+* For full copyright and license information, please see
+* the docs/CREDITS.txt file.
+*
+*/
+
+/**
+* @group functional
+*/
+class phpbb_functional_acp_avatar_settings_test extends phpbb_functional_test_case
+{
+	public function test_avatar_upload_settings()
+	{
+		$this->add_lang(['acp/common', 'acp/board']);
+		$this->login();
+		$this->admin_login();
+
+		$crawler = self::request('GET', 'adm/index.php?i=acp_board&mode=avatar&sid=' . $this->sid);
+		$this->assertContainsLang('ACP_AVATAR_SETTINGS', $this->get_content());
+		$this->assertContainsLang('ACP_AVATAR_SETTINGS_EXPLAIN', $this->get_content());
+
+		// Test disabling avatar uploading - valid
+		$form = $crawler->selectButton($this->lang('SUBMIT'))->form([
+			'config[allow_avatar_upload]' => '0'
+		]);
+		$crawler = self::submit($form);
+		$this->assertContainsLang('CONFIG_UPDATED', $crawler->filter('div[class="successbox"] > p')->text());
+
+		$crawler = self::request('GET', 'adm/index.php?i=acp_board&mode=avatar&sid=' . $this->sid);
+
+		// Test enabling avatar uploading - valid
+		$form = $crawler->selectButton($this->lang('SUBMIT'))->form([
+			'config[allow_avatar_upload]' => '1'
+		]);
+		$crawler = self::submit($form);
+		$this->assertContainsLang('CONFIG_UPDATED', $crawler->filter('div[class="successbox"] > p')->text());
+
+		$crawler = self::request('GET', 'adm/index.php?i=acp_board&mode=avatar&sid=' . $this->sid);
+
+		// Test empty avatar storage path while avatar uploading is enabled - invalid
+		$form = $crawler->selectButton($this->lang('SUBMIT'))->form([
+			'config[avatar_path]' => ''
+		]);
+		$crawler = self::submit($form);
+		$this->assertContainsLang('WARNING', $crawler->filter('div[class="errorbox"] > h3')->text());
+		$this->assertContainsLang('AVATAR_NO_UPLOAD_PATH', $crawler->filter('div[class="errorbox"] > p')->text());
+
+		// Test avatar upload path became not writable on the server afterwards
+		// Unix tests only
+		if (!defined('PHP_WINDOWS_VERSION_MAJOR'))
+		{
+			$crawler = self::request('GET', 'adm/index.php?i=acp_board&mode=avatar&sid=' . $this->sid);
+			$form = $crawler->selectButton($this->lang('SUBMIT'))->form();
+			$values = $form->getValues();
+			$avatar_upload_path = $values['config[avatar_path]'];
+			$filesystem = new \phpbb\filesystem\filesystem;
+			// Make the directory not writable
+			global $phpbb_root_path;
+			$filesystem->chmod($phpbb_root_path . $avatar_upload_path, 444);
+			$this->assertFalse($filesystem->is_writable($phpbb_root_path . $avatar_upload_path));
+
+			// Visit Avatar ACP settings again - warning should be displayed
+			$crawler = self::request('GET', 'adm/index.php?i=acp_board&mode=avatar&sid=' . $this->sid);
+			$this->assertContainsLang('WARNING', $crawler->filter('div[class="errorbox"] > h3')->text());
+			$this->assertContainsLang('AVATAR_NO_UPLOAD_DIR', $crawler->filter('div[class="errorbox"] > p')->text());
+			
+			// Restore default state
+			$filesystem->chmod($phpbb_root_path . $avatar_upload_path, 777);
+			$this->assertTrue($filesystem->is_writable($phpbb_root_path . $avatar_upload_path));
+
+			$crawler = self::request('GET', 'adm/index.php?i=acp_board&mode=avatar&sid=' . $this->sid);
+			$this->assertNotContainsLang('AVATAR_NO_UPLOAD_DIR', $this->get_content());
+			$this->assertNotContainsLang('AVATAR_NO_UPLOAD_PATH', $this->get_content());
+		}
+	}
+}