diff --git a/phpBB/docs/CHANGELOG.html b/phpBB/docs/CHANGELOG.html
index 3646b82a0b..7b9705bd8c 100644
--- a/phpBB/docs/CHANGELOG.html
+++ b/phpBB/docs/CHANGELOG.html
@@ -231,7 +231,7 @@ p a {
 		<li>Limit maximum number of allowed characters in messages to 60.000 by default. Admins should increase their PHP time limits if they want to raise this tremedously.</li>
 		<li>Some changes to the conversion documentation</li>
 		<li>[Fix] Only use permissions from existing forums during the conversion (Bug #11417)</li>
-
+		<li>[Fix] Do not permit the decimal as a valid prefix character (Bug #11967)</li>
 	</ul>
 
 	</div>
diff --git a/phpBB/includes/functions_install.php b/phpBB/includes/functions_install.php
index 43d536e7e9..fa85b89d48 100644
--- a/phpBB/includes/functions_install.php
+++ b/phpBB/includes/functions_install.php
@@ -280,7 +280,7 @@ function connect_check_db($error_connect, &$error, $dbms, $table_prefix, $dbhost
 	{
 		case 'mysql':
 		case 'mysqli':
-			if (strpos($table_prefix, '-') !== false)
+			if (strpos($table_prefix, '-') !== false || strpos($table_prefix, '.') !== false)
 			{
 				$error[] = $lang['INST_ERR_PREFIX_INVALID'];
 				return false;