diff --git a/src/DataObjects/AbstractCmisObject.php b/src/DataObjects/AbstractCmisObject.php
index <HASH>..<HASH> 100644
--- a/src/DataObjects/AbstractCmisObject.php
+++ b/src/DataObjects/AbstractCmisObject.php
@@ -459,12 +459,12 @@ abstract class AbstractCmisObject implements CmisObjectInterface
      */
     public function getBaseTypeId()
     {
-        $baseType = $this->getProperty(PropertyIds::BASE_TYPE_ID);
-        if ($baseType === null) {
+        $baseTypeProperty = $this->getProperty(PropertyIds::BASE_TYPE_ID);
+        if ($baseTypeProperty === null) {
             return null;
         }
 
-        return BaseTypeId::cast($baseType);
+        return BaseTypeId::cast($baseTypeProperty->getFirstValue());
     }
 
     /**
Fix bug in AbstractCmisObject::getBaseTypeId

Summary:
In `AbstractCmisObject::getBaseTypeId` the property object
has been passed to the `BaseTypeId` enumeration and not the expected
string value of the property.

Reviewers: dkd-ebert, #forgetit-dev

Reviewed By: dkd-ebert, #forgetit-dev

Differential Revision: <URL>