diff --git a/libraries/object-persistor/src/FSPersistor.js b/libraries/object-persistor/src/FSPersistor.js
index 4afc1cbb4a..058017038b 100644
--- a/libraries/object-persistor/src/FSPersistor.js
+++ b/libraries/object-persistor/src/FSPersistor.js
@@ -1,3 +1,4 @@
+const crypto = require('crypto')
 const fs = require('fs')
 const fsPromises = require('fs/promises')
 const globCallbacks = require('glob')
@@ -41,30 +42,16 @@ module.exports = class FSPersistor extends AbstractPersistor {
       await this._ensureDirectoryExists(targetPath)
       const tempFilePath = await this._writeStreamToTempFile(
         location,
-        sourceStream
+        sourceStream,
+        opts
       )
 
       try {
-        if (opts.sourceMd5) {
-          const actualMd5 = await _getFileMd5HashForPath(tempFilePath)
-          if (actualMd5 !== opts.sourceMd5) {
-            throw new WriteError('md5 hash mismatch', {
-              location,
-              target,
-              expectedMd5: opts.sourceMd5,
-              actualMd5,
-            })
-          }
-        }
-
         await fsPromises.rename(tempFilePath, targetPath)
       } finally {
         await this._cleanupTempFile(tempFilePath)
       }
     } catch (err) {
-      if (err instanceof WriteError) {
-        throw err
-      }
       throw PersistorHelper.wrapError(
         err,
         'failed to write stream',
@@ -116,7 +103,9 @@ module.exports = class FSPersistor extends AbstractPersistor {
   async getObjectMd5Hash(location, filename) {
     const fsPath = this._getFsPath(location, filename)
     try {
-      return await _getFileMd5HashForPath(fsPath)
+      const stream = fs.createReadStream(fsPath)
+      const hash = await PersistorHelper.calculateStreamMd5(stream)
+      return hash
     } catch (err) {
       throw new ReadError(
         'unable to get md5 hash from file',
@@ -231,30 +220,49 @@ module.exports = class FSPersistor extends AbstractPersistor {
     return size
   }
 
-  async _writeStreamToTempFile(location, stream) {
+  async _writeStreamToTempFile(location, stream, opts = {}) {
     const tempDirPath = await fsPromises.mkdtemp(Path.join(location, 'tmp-'))
     const tempFilePath = Path.join(tempDirPath, 'uploaded-file')
 
+    const transforms = []
+    let md5Observer
+    if (opts.sourceMd5) {
+      md5Observer = createMd5Observer()
+      transforms.push(md5Observer.transform)
+    }
+
     let timer
     if (this.metrics) {
       timer = new this.metrics.Timer('writingFile')
     }
 
-    const writeStream = fs.createWriteStream(tempFilePath)
     try {
-      await pipeline(stream, writeStream)
+      const writeStream = fs.createWriteStream(tempFilePath)
+      await pipeline(stream, ...transforms, writeStream)
       if (timer) {
         timer.done()
       }
-      return tempFilePath
     } catch (err) {
-      await fsPromises.rm(tempFilePath, { force: true })
+      await this._cleanupTempFile(tempFilePath)
       throw new WriteError(
         'problem writing temp file locally',
-        { err, tempFilePath },
+        { tempFilePath },
         err
       )
     }
+
+    if (opts.sourceMd5) {
+      const actualMd5 = md5Observer.hash.digest('hex')
+      if (actualMd5 !== opts.sourceMd5) {
+        await this._cleanupTempFile(tempFilePath)
+        throw new WriteError('md5 hash mismatch', {
+          expectedMd5: opts.sourceMd5,
+          actualMd5,
+        })
+      }
+    }
+
+    return tempFilePath
   }
 
   async _cleanupTempFile(tempFilePath) {
@@ -283,7 +291,15 @@ module.exports = class FSPersistor extends AbstractPersistor {
   }
 }
 
-async function _getFileMd5HashForPath(fullPath) {
-  const stream = fs.createReadStream(fullPath)
-  return PersistorHelper.calculateStreamMd5(stream)
+function createMd5Observer() {
+  const hash = crypto.createHash('md5')
+
+  async function* transform(chunks) {
+    for await (const chunk of chunks) {
+      hash.update(chunk)
+      yield chunk
+    }
+  }
+
+  return { hash, transform }
 }
diff --git a/libraries/object-persistor/test/unit/FSPersistorTests.js b/libraries/object-persistor/test/unit/FSPersistorTests.js
index c8e7172218..220c7f95e4 100644
--- a/libraries/object-persistor/test/unit/FSPersistorTests.js
+++ b/libraries/object-persistor/test/unit/FSPersistorTests.js
@@ -147,7 +147,7 @@ describe('FSPersistorTests', function () {
                 persistor.sendStream(location, files.wombat, stream, {
                   sourceMd5: md5('wrong content'),
                 })
-              ).to.be.rejectedWith(Errors.WriteError, 'md5 hash mismatch')
+              ).to.be.rejectedWith(Errors.WriteError)
             })
 
             it('should not write the target file', async function () {
@@ -236,7 +236,7 @@ describe('FSPersistorTests', function () {
                 persistor.sendStream(location, files.wombat, stream, {
                   sourceMd5: md5('wrong content'),
                 })
-              ).to.be.rejectedWith(Errors.WriteError, 'md5 hash mismatch')
+              ).to.be.rejectedWith(Errors.WriteError)
             })
 
             it('should not update the target file', async function () {