diff --git a/test/fixtures/build.gradle b/test/fixtures/build.gradle
index 02d68517903a3..e69de29bb2d1d 100644
--- a/test/fixtures/build.gradle
+++ b/test/fixtures/build.gradle
@@ -1,9 +0,0 @@
-
-subprojects {
-  // fixtures don't have tests, these are external projects used by the build
-  pluginManager.withPlugin('java') {
-    tasks.named('test').configure {
-      enabled = false
-    }
-  }
-}
diff --git a/test/fixtures/s3-fixture/src/test/java/fixture/s3/S3HttpHandlerTests.java b/test/fixtures/s3-fixture/src/test/java/fixture/s3/S3HttpHandlerTests.java
index 375f428f748e6..58f32292fa91c 100644
--- a/test/fixtures/s3-fixture/src/test/java/fixture/s3/S3HttpHandlerTests.java
+++ b/test/fixtures/s3-fixture/src/test/java/fixture/s3/S3HttpHandlerTests.java
@@ -31,6 +31,8 @@
 import java.util.List;
 import java.util.Objects;
 
+import static org.hamcrest.Matchers.allOf;
+import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.greaterThan;
 
 public class S3HttpHandlerTests extends ESTestCase {
@@ -261,7 +263,7 @@ public void testListAndAbortMultipartUpload() {
             <Delimiter /><Prefix>path/blob</Prefix><MaxUploads>10000</MaxUploads><IsTruncated>false</IsTruncated>\
             </ListMultipartUploadsResult>"""), handleRequest(handler, "GET", "/bucket/?uploads&prefix=path/blob"));
 
-        assertEquals(RestStatus.NOT_FOUND, handleRequest(handler, "POST", "/bucket/path/blob?uploadId=" + uploadId, Strings.format("""
+        final var completeUploadResponse = handleRequest(handler, "POST", "/bucket/path/blob?uploadId=" + uploadId, Strings.format("""
             <?xml version="1.0" encoding="UTF-8"?>
             <CompleteMultipartUpload xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
                <Part>
@@ -272,7 +274,13 @@ public void testListAndAbortMultipartUpload() {
                   <ETag>%s</ETag>
                   <PartNumber>2</PartNumber>
                </Part>
-            </CompleteMultipartUpload>""", part1Etag, part2Etag)).status());
+            </CompleteMultipartUpload>""", part1Etag, part2Etag));
+        if (completeUploadResponse.status() == RestStatus.OK) {
+            // possible, but rare, indicating that S3 started processing the upload before returning an error
+            assertThat(completeUploadResponse.body().utf8ToString(), allOf(containsString("<Error>"), containsString("NoSuchUpload")));
+        } else {
+            assertEquals(RestStatus.NOT_FOUND, completeUploadResponse.status());
+        }
     }
 
     private static String getUploadId(BytesReference createUploadResponseBody) {