diff --git a/phpBB/phpbb/console/command/fixup/update_hashes.php b/phpBB/phpbb/console/command/fixup/update_hashes.php
index 05bef48c92..b1ffa2159b 100644
--- a/phpBB/phpbb/console/command/fixup/update_hashes.php
+++ b/phpBB/phpbb/console/command/fixup/update_hashes.php
@@ -101,6 +101,14 @@ class update_hashes extends \phpbb\console\command\command
 		while ($row = $this->db->sql_fetchrow($result))
 		{
 			$old_hash = preg_replace('/^\$CP\$/', '', $row['user_password']);
+
+			// If stored hash type is unknown then it's md5 hash with no prefix
+			// First rehash it using $H$ as hash type identifier (salted_md5)
+			if (!$this->passwords_manager->detect_algorithm($old_hash))
+			{
+				$old_hash = $this->passwords_manager->hash($old_hash, '$H$');
+			}
+
 			$new_hash = $this->passwords_manager->hash($old_hash, [$this->default_type]);
 
 			$sql = 'UPDATE ' . USERS_TABLE . "
diff --git a/phpBB/phpbb/cron/task/core/update_hashes.php b/phpBB/phpbb/cron/task/core/update_hashes.php
index 61ed0d0501..78221bb35f 100644
--- a/phpBB/phpbb/cron/task/core/update_hashes.php
+++ b/phpBB/phpbb/cron/task/core/update_hashes.php
@@ -107,6 +107,14 @@ class update_hashes extends \phpbb\cron\task\base
 			while ($row = $this->db->sql_fetchrow($result))
 			{
 				$old_hash = preg_replace('/^\$CP\$/', '', $row['user_password']);
+
+				// If stored hash type is unknown then it's md5 hash with no prefix
+				// First rehash it using $H$ as hash type identifier (salted_md5)
+				if (!$this->passwords_manager->detect_algorithm($old_hash))
+				{
+					$old_hash = $this->passwords_manager->hash($old_hash, '$H$');
+				}
+
 				$new_hash = $this->passwords_manager->hash($old_hash, [$this->default_type]);
 
 				// Increase number so we know that users were selected from the database