diff --git a/google-cloud-storage/src/main/java/com/google/cloud/storage/ParallelCompositeUploadBlobWriteSessionConfig.java b/google-cloud-storage/src/main/java/com/google/cloud/storage/ParallelCompositeUploadBlobWriteSessionConfig.java
index b877d82d9..e13f54964 100644
--- a/google-cloud-storage/src/main/java/com/google/cloud/storage/ParallelCompositeUploadBlobWriteSessionConfig.java
+++ b/google-cloud-storage/src/main/java/com/google/cloud/storage/ParallelCompositeUploadBlobWriteSessionConfig.java
@@ -612,7 +612,10 @@ public NoPrefix(SecureRandom rand) {
       }
 
       @Override
-      protected String fmtFields(String randomKey, String nameDigest, String partRange) {
+      protected String fmtFields(String randomKey, String ultimateObjectName, String partRange) {
+        HashCode hashCode =
+            OBJECT_NAME_HASH_FUNCTION.hashString(ultimateObjectName, StandardCharsets.UTF_8);
+        String nameDigest = B64.encodeToString(hashCode.asBytes());
         return randomKey
             + FIELD_SEPARATOR
             // todo: do we want to
diff --git a/google-cloud-storage/src/test/java/com/google/cloud/storage/ParallelCompositeUploadBlobWriteSessionConfigTest.java b/google-cloud-storage/src/test/java/com/google/cloud/storage/ParallelCompositeUploadBlobWriteSessionConfigTest.java
index 86eddc5b9..465741a7d 100644
--- a/google-cloud-storage/src/test/java/com/google/cloud/storage/ParallelCompositeUploadBlobWriteSessionConfigTest.java
+++ b/google-cloud-storage/src/test/java/com/google/cloud/storage/ParallelCompositeUploadBlobWriteSessionConfigTest.java
@@ -84,7 +84,7 @@ public void partNameStrategy_objectNamePrefix() throws Exception {
         // name digest
         () -> assertField(fmt, 1).hasLength(22),
         () -> assertField(fmt, 2).isEqualTo("0001-0096.part"),
-        () -> assertThat(fmt).startsWith("a/b/obj/"));
+        () -> assertThat(fmt).startsWith("a/b/obj"));
   }
 
   private static StringSubject assertField(String fmt, int idx) {