diff --git a/system/Model.php b/system/Model.php
index 5b413ad79ad7..429ac86b9463 100644
--- a/system/Model.php
+++ b/system/Model.php
@@ -1233,7 +1233,7 @@ public function validate($data): bool
 		// or an array of rules.
 		if (is_string($this->validationRules))
 		{
-			$valid = $this->validation->run($data, $this->validationRules);
+			$valid = $this->validation->run($data, $this->validationRules, $this->DBGroup);
 		}
 		else
 		{
@@ -1241,7 +1241,7 @@ public function validate($data): bool
 			// the value found in $data, if exists.
 			$rules = $this->fillPlaceholders($this->validationRules, $data);
 
-			$this->validation->setRules($rules, $this->validationMessages);
+			$this->validation->setRules($rules, $this->validationMessages, $this->DBGroup);
 			$valid = $this->validation->run($data);
 		}
 
diff --git a/system/Validation/Rules.php b/system/Validation/Rules.php
index bcf1a83f52fb..8e259436695d 100644
--- a/system/Validation/Rules.php
+++ b/system/Validation/Rules.php
@@ -157,7 +157,7 @@ public function is_unique(string $str = null, string $field, array $data): bool
 		// Break the table and field apart
 		sscanf($field, '%[^.].%[^.]', $table, $field);
 
-		$db = Database::connect();
+		$db = Database::connect($data['DBGroup'] ?? null);
 		
 		$row = $db->table($table)
 				  ->select('1')
diff --git a/system/Validation/Validation.php b/system/Validation/Validation.php
index 25bf46818cc4..5f10cb34ab0d 100644
--- a/system/Validation/Validation.php
+++ b/system/Validation/Validation.php
@@ -123,10 +123,13 @@ public function __construct($config, RendererInterface $view)
 	 *
 	 * @return bool
 	 */
-	public function run(array $data = null, string $group = null): bool
+	public function run(array $data = null, string $group = null, string $db_group = null): bool
 	{
 		$data = $data ?? $this->data;
 
+		// i.e. is_unique
+		$data['DBGroup'] = $db_group;
+
 		$this->loadRuleSets();
 
 		$this->loadRuleGroup($group);