diff --git a/phpBB/docs/CHANGELOG.html b/phpBB/docs/CHANGELOG.html
index 571b23cb47..ab863d7fc6 100644
--- a/phpBB/docs/CHANGELOG.html
+++ b/phpBB/docs/CHANGELOG.html
@@ -290,7 +290,7 @@ p a {
 		<li>[Fix] Fix sorting by author on "unanswered posts" (Bug #12545)</li>
 		<li>[Fix] Allow searching for multibyte authors (Bug #11793)</li>
 		<li>[Fix] Writing directories/files with correct permissions using FTP for transfers on PHP4</li>
-
+		<li>[Fix] Oracle sequences during conversions are now corrected (Bug #12555)</li>
 	</ul>
 
 	</div>
diff --git a/phpBB/install/convertors/functions_phpbb20.php b/phpBB/install/convertors/functions_phpbb20.php
index ec282c8f46..eca72b64bd 100644
--- a/phpBB/install/convertors/functions_phpbb20.php
+++ b/phpBB/install/convertors/functions_phpbb20.php
@@ -287,6 +287,20 @@ function phpbb_insert_forums()
 		case 'mssql_odbc':
 			$db->sql_query('SET IDENTITY_INSERT ' . FORUMS_TABLE . ' OFF');
 		break;
+
+		case 'oracle':
+			$result = $db->sql_query('SELECT MAX(forum_id) as max_id FROM ' . FORUMS_TABLE);
+			$row = $db->sql_fetchrow($result);
+			$db->sql_freeresult($result);
+
+			$largest_id = (int) $row['max_id'];
+
+			if ($largest_id)
+			{
+				$db->sql_query('DROP SEQUENCE ' . FORUMS_TABLE . '_seq');
+				$db->sql_query('CREATE SEQUENCE ' . FORUMS_TABLE . '_seq START WITH ' . ($largest_id + 1));
+			}
+		break;
 	}
 }
 
diff --git a/phpBB/install/install_convert.php b/phpBB/install/install_convert.php
index 455f8841ad..4d7055d763 100644
--- a/phpBB/install/install_convert.php
+++ b/phpBB/install/install_convert.php
@@ -1112,6 +1112,20 @@ class install_convert extends module
 						case 'postgres':
 							$db->sql_query("SELECT SETVAL('" . $schema['target'] . "_seq',(select case when max(" . $schema['autoincrement'] . ")>0 then max(" . $schema['autoincrement'] . ")+1 else 1 end from " . $schema['target'] . '));');
 						break;
+
+						case 'oracle':
+							$result = $db->sql_query('SELECT MAX(' . $schema['autoincrement'] . ') as max_id FROM ' . $schema['target']);
+							$row = $db->sql_fetchrow($result);
+							$db->sql_freeresult($result);
+
+							$largest_id = (int) $row['max_id'];
+
+							if ($largest_id)
+							{
+								$db->sql_query('DROP SEQUENCE ' . $schema['target'] . '_seq');
+								$db->sql_query('CREATE SEQUENCE ' . $schema['target'] . '_seq START WITH ' . ($largest_id + 1));
+							}
+						break;
 					}
 				}
 			}
@@ -1367,6 +1381,20 @@ class install_convert extends module
 						case 'postgres':
 							$db->sql_query("SELECT SETVAL('" . $schema['target'] . "_seq',(select case when max(" . $schema['autoincrement'] . ")>0 then max(" . $schema['autoincrement'] . ")+1 else 1 end from " . $schema['target'] . '));');
 						break;
+
+						case 'oracle':
+							$result = $db->sql_query('SELECT MAX(' . $schema['autoincrement'] . ') as max_id FROM ' . $schema['target']);
+							$row = $db->sql_fetchrow($result);
+							$db->sql_freeresult($result);
+
+							$largest_id = (int) $row['max_id'];
+
+							if ($largest_id)
+							{
+								$db->sql_query('DROP SEQUENCE ' . $schema['target'] . '_seq');
+								$db->sql_query('CREATE SEQUENCE ' . $schema['target'] . '_seq START WITH ' . ($largest_id + 1));
+							}
+						break;
 					}
 				}
 			}