diff --git a/.changeset/twenty-crews-punch.md b/.changeset/twenty-crews-punch.md
new file mode 100644
index 00000000..d16faec3
--- /dev/null
+++ b/.changeset/twenty-crews-punch.md
@@ -0,0 +1,5 @@
+---
+"@tus/s3-store": patch
+---
+
+Fix unhandled promise rejection when uploading a part fails, in which case we returned too early, leaving other parts running in the background.
diff --git a/packages/s3-store/package.json b/packages/s3-store/package.json
index e913379a..c58be208 100644
--- a/packages/s3-store/package.json
+++ b/packages/s3-store/package.json
@@ -16,6 +16,7 @@
   ],
   "scripts": {
     "build": "tsc --build",
+    "pretest": "tsc --build",
     "test": "mocha --timeout 40000 --exit --extension ts --require ts-node/register"
   },
   "dependencies": {
diff --git a/packages/s3-store/src/index.ts b/packages/s3-store/src/index.ts
index 40e1367c..5009c602 100644
--- a/packages/s3-store/src/index.ts
+++ b/packages/s3-store/src/index.ts
@@ -409,19 +409,25 @@ export class S3Store extends DataStore {
             bytesUploaded += partSize
             resolve()
           } catch (error) {
+            // If there's an error, destroy the splitter to stop processing more chunks
+            splitterStream.destroy(error)
             reject(error)
           } finally {
             fsProm.rm(path).catch(() => {
               /* ignore */
             })
-            acquiredPermit?.release()
+            acquiredPermit?.release().catch(() => {
+              /* ignore */
+            })
           }
         })
 
         promises.push(deferred)
       })
       .on('chunkError', () => {
-        permit?.release()
+        permit?.release().catch(() => {
+          /* ignore */
+        })
       })
 
     try {
@@ -437,6 +443,10 @@ export class S3Store extends DataStore {
 
       promises.push(Promise.reject(error))
     } finally {
+      // Wait for all promises. We don't want to return
+      // early have have promises running in the background.
+      await Promise.allSettled(promises)
+      // But we do want to reject the promise if any of the promises reject.
       await Promise.all(promises)
     }
 
diff --git a/packages/s3-store/test/index.ts b/packages/s3-store/test/index.ts
index 4a8e31af..e9042100 100644
--- a/packages/s3-store/test/index.ts
+++ b/packages/s3-store/test/index.ts
@@ -278,14 +278,14 @@ describe('S3DataStore', () => {
     }
   })
 
-  it('should use default maxMultipartParts when not specified', function () {
+  it('should use default maxMultipartParts when not specified', () => {
     const store = new S3Store({
       s3ClientConfig,
     })
     assert.equal(store.maxMultipartParts, 10000)
   })
 
-  it('should use custom maxMultipartParts when specified', function () {
+  it('should use custom maxMultipartParts when specified', () => {
     const customMaxParts = 5000
     const store = new S3Store({
       s3ClientConfig,
@@ -294,6 +294,38 @@ describe('S3DataStore', () => {
     assert.equal(store.maxMultipartParts, customMaxParts)
   })
 
+  it('should handle multiple concurrent part uploads with some failures', async () => {
+    const store = new S3Store({
+      partSize: 5 * 1024 * 1024,
+      maxConcurrentPartUploads: 3, // Allow 3 concurrent uploads
+      s3ClientConfig,
+    })
+
+    const size = 15 * 1024 * 1024 // 15MB will be split into 3 parts
+    const upload = new Upload({
+      id: shared.testId('concurrent-failures'),
+      size,
+      offset: 0,
+    })
+
+    // @ts-expect-error private method
+    const uploadPartStub = sinon.stub(store, 'uploadPart')
+
+    // Make the second part upload fail
+    uploadPartStub.onCall(0).resolves('etag1')
+    uploadPartStub.onCall(1).rejects(new Error('Part 2 upload failed'))
+    uploadPartStub.onCall(2).resolves('etag3')
+
+    await store.create(upload)
+
+    try {
+      await store.write(Readable.from(Buffer.alloc(size)), upload.id, upload.offset)
+      assert.fail('Expected write to fail but it succeeded')
+    } catch (error) {
+      assert.equal(uploadPartStub.callCount, 2, '2 parts should have been attempted')
+    }
+  })
+
   shared.shouldHaveStoreMethods()
   shared.shouldCreateUploads()
   shared.shouldRemoveUploads() // Termination extension