diff --git a/src/Type/ObjectType.php b/src/Type/ObjectType.php
index 7f18546d3e..1fd2236087 100644
--- a/src/Type/ObjectType.php
+++ b/src/Type/ObjectType.php
@@ -456,12 +456,12 @@ private function checkSubclassAcceptability(string $thatClass): AcceptsResult
 
 		if ($thisReflection->isInterface() && $thatReflection->isInterface()) {
 			return AcceptsResult::createFromBoolean(
-				$thatReflection->implementsInterface($this->className),
+				$thatReflection->implementsInterface($thisReflection->getName()),
 			);
 		}
 
 		return AcceptsResult::createFromBoolean(
-			$thatReflection->isSubclassOf($this->className),
+			$thatReflection->isSubclassOf($thisReflection->getName()),
 		);
 	}