diff --git a/CloudObjects/SDK/CloudObject.php b/CloudObjects/SDK/CloudObject.php
index c4da858..70278d0 100644
--- a/CloudObjects/SDK/CloudObject.php
+++ b/CloudObjects/SDK/CloudObject.php
@@ -157,6 +157,13 @@ class CloudObject {
         }
 
         return $this->retriever->getObjectNode($coid);
-    }    
+    }
+    
+    /**
+     * Get the revision of the object.
+     */
+    public function getRevision() : string {
+        return $this->getString(Constants::PROPERTY_REVISION);
+    }
 
 }
diff --git a/CloudObjects/SDK/Constants.php b/CloudObjects/SDK/Constants.php
new file mode 100644
index 0000000..12ab01d
--- /dev/null
+++ b/CloudObjects/SDK/Constants.php
@@ -0,0 +1,13 @@
+<?php
+
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+ 
+namespace CloudObjects\SDK;
+
+class Constants {
+
+    const PROPERTY_REVISION = 'coid://cloudobjects.io/isAtRevision';
+
+}
\ No newline at end of file
diff --git a/CloudObjects/SDK/ObjectRetriever.php b/CloudObjects/SDK/ObjectRetriever.php
index 1144732..d27bfe2 100644
--- a/CloudObjects/SDK/ObjectRetriever.php
+++ b/CloudObjects/SDK/ObjectRetriever.php
@@ -32,9 +32,7 @@ class ObjectRetriever implements CustomCacheAndLogInterface {
 	private $defaultReader;
 
 	const CO_API_URL = 'https://od.coid.link/';
-	
-	const REVISION_PROPERTY = 'coid://cloudobjects.io/isAtRevision';
-
+		
 	public function __construct($options = []) {
 		// Merge options with defaults
 		$this->options = array_merge([
@@ -479,7 +477,7 @@ class ObjectRetriever implements CustomCacheAndLogInterface {
 		}
 
 		if (!isset($fileData)
-				|| $fileRevision!=$object->getProperty(self::REVISION_PROPERTY)->getValue()) {
+				|| $fileRevision !== $object->getProperty(Constants::PROPERTY_REVISION)->getValue()) {
 
 			// Does not exist in cache or is outdated, fetch from CloudObjects
 			try {
@@ -487,7 +485,7 @@ class ObjectRetriever implements CustomCacheAndLogInterface {
 					.'/'.basename($filename));
 
 				$fileContent = $response->getBody()->getContents();
-				$fileData = $object->getProperty(self::REVISION_PROPERTY)->getValue().'#'.$fileContent;
+				$fileData = $object->getProperty(Constants::PROPERTY_REVISION)->getValue().'#'.$fileContent;
 				$this->putIntoCache($cacheId, $fileData, 0);
 
 				$this->logInfoWithTime('Fetched attachment <'.$filename.'> for <'.$object->getId().'> from Core API ['.$response->getStatusCode().'].', $ts);