diff --git a/libraries/object-persistor/src/GcsPersistor.js b/libraries/object-persistor/src/GcsPersistor.js
index 90c02ee886..94b77ba8b8 100644
--- a/libraries/object-persistor/src/GcsPersistor.js
+++ b/libraries/object-persistor/src/GcsPersistor.js
@@ -180,7 +180,7 @@ module.exports = class GcsPersistor extends AbstractPersistor {
         .bucket(bucketName)
         .file(key)
         .getMetadata()
-      return metadata.size
+      return parseInt(metadata.size, 10)
     } catch (err) {
       throw PersistorHelper.wrapError(
         err,
@@ -289,7 +289,10 @@ module.exports = class GcsPersistor extends AbstractPersistor {
       )
     }
 
-    return files.reduce((acc, file) => Number(file.metadata.size) + acc, 0)
+    return files.reduce(
+      (acc, file) => parseInt(file.metadata.size, 10) + acc,
+      0
+    )
   }
 
   async checkIfObjectExists(bucketName, key) {
diff --git a/libraries/object-persistor/test/unit/GcsPersistorTests.js b/libraries/object-persistor/test/unit/GcsPersistorTests.js
index f9b31fa72b..4d16bd4ca5 100644
--- a/libraries/object-persistor/test/unit/GcsPersistorTests.js
+++ b/libraries/object-persistor/test/unit/GcsPersistorTests.js
@@ -45,11 +45,11 @@ describe('GcsPersistorTests', function () {
 
     files = [
       {
-        metadata: { size: 11, md5Hash: '/////wAAAAD/////AAAAAA==' },
+        metadata: { size: '11', md5Hash: '/////wAAAAD/////AAAAAA==' },
         delete: sinon.stub(),
       },
       {
-        metadata: { size: 22, md5Hash: '/////wAAAAD/////AAAAAA==' },
+        metadata: { size: '22', md5Hash: '/////wAAAAD/////AAAAAA==' },
         delete: sinon.stub(),
       },
     ]
@@ -302,7 +302,7 @@ describe('GcsPersistorTests', function () {
       })
 
       it('should return the object size', function () {
-        expect(size).to.equal(files[0].metadata.size)
+        expect(size).to.equal(11)
       })
 
       it('should pass the bucket and key to GCS', function () {
diff --git a/services/filestore/test/acceptance/js/FilestoreTests.js b/services/filestore/test/acceptance/js/FilestoreTests.js
index af67afe20b..6984be4caf 100644
--- a/services/filestore/test/acceptance/js/FilestoreTests.js
+++ b/services/filestore/test/acceptance/js/FilestoreTests.js
@@ -1354,6 +1354,25 @@ describe('Filestore', function () {
         })
       })
 
+      describe('getObjectSize', function () {
+        it('should return a number', async function () {
+          const buf = Buffer.from('hello')
+          const fileId = new ObjectId().toString()
+          const fileUrl = `${filestoreUrl}/project/${projectId}/file/${fileId}`
+          const res = await fetch(fileUrl, {
+            method: 'POST',
+            body: Stream.Readable.from([buf]),
+          })
+          if (!res.ok) throw new Error(res.statusText)
+          expect(
+            await app.persistor.getObjectSize(
+              Settings.filestore.stores.user_files,
+              `${projectId}/${fileId}`
+            )
+          ).to.equal(buf.byteLength)
+        })
+      })
+
       describe('checkIfObjectExists', function () {
         it('should return false when the object does not exist', async function () {
           expect(