diff --git a/phpBB/docs/CHANGELOG.html b/phpBB/docs/CHANGELOG.html
index 067a2c88e4..c6143196c2 100644
--- a/phpBB/docs/CHANGELOG.html
+++ b/phpBB/docs/CHANGELOG.html
@@ -89,6 +89,7 @@
 		<li>[Fix] Fixed blank style on setups having no username defined within config.php (Bug #25065)</li>
 		<li>[Fix] Made the compress_tar class tolerate archives that do not properly have their archived contents listed (Bug #14429 / thanks to JRSweets for his patch)</li>
 		<li>[Fix] Moved topics should not count towards the number of topics in a forum (Bug #14648 / thanks to Schumi for his patch)</li>
+		<li>[Fix] Properly check for invalid characters in MySQL DB prefixes during install (Bug #18775)</li>
 	</ul>
 
 	<a name="v300"></a><h3>1.ii. Changes since 3.0.0</h3>
diff --git a/phpBB/includes/functions_install.php b/phpBB/includes/functions_install.php
index f43ef7c5c7..90459813f1 100644
--- a/phpBB/includes/functions_install.php
+++ b/phpBB/includes/functions_install.php
@@ -286,7 +286,7 @@ function connect_check_db($error_connect, &$error, $dbms_details, $table_prefix,
 	{
 		case 'mysql':
 		case 'mysqli':
-			if (strpos($table_prefix, '-') !== false || strpos($table_prefix, '.') !== false)
+			if (strspn($table_prefix, '-./\\') !== 0)
 			{
 				$error[] = $lang['INST_ERR_PREFIX_INVALID'];
 				return false;