diff --git a/moto/s3/responses.py b/moto/s3/responses.py
index b3ce38005..1a71f8382 100644
--- a/moto/s3/responses.py
+++ b/moto/s3/responses.py
@@ -1556,7 +1556,8 @@ class S3Response(BaseResponse):
         new_key.website_redirect_location = request.headers.get(
             "x-amz-website-redirect-location"
         )
-        new_key.checksum_algorithm = checksum_algorithm
+        if checksum_algorithm:
+            new_key.checksum_algorithm = checksum_algorithm
         self.backend.set_key_tags(new_key, tagging)
 
         response_headers.update(new_key.response_dict)
diff --git a/tests/test_s3/test_s3.py b/tests/test_s3/test_s3.py
index 3549cc19f..3ebee03fd 100644
--- a/tests/test_s3/test_s3.py
+++ b/tests/test_s3/test_s3.py
@@ -1400,6 +1400,11 @@ def test_list_objects_v2_truncate_combined_keys_and_folders():
 def test_list_objects_v2_checksum_algo():
     s3 = boto3.client("s3", region_name=DEFAULT_REGION_NAME)
     s3.create_bucket(Bucket="mybucket")
+    resp = s3.put_object(Bucket="mybucket", Key="0", Body="a")
+    resp.should_not.have.key("ChecksumCRC32")
+    resp["ResponseMetadata"]["HTTPHeaders"].should_not.have.key(
+        "x-amz-sdk-checksum-algorithm"
+    )
     resp = s3.put_object(
         Bucket="mybucket", Key="1", Body="a", ChecksumAlgorithm="CRC32"
     )
@@ -1416,8 +1421,9 @@ def test_list_objects_v2_checksum_algo():
     ].should.equal("SHA256")
 
     resp = s3.list_objects_v2(Bucket="mybucket")["Contents"]
-    resp[0].should.have.key("ChecksumAlgorithm").equals(["CRC32"])
-    resp[1].should.have.key("ChecksumAlgorithm").equals(["SHA256"])
+    resp[0].should_not.have.key("ChecksumAlgorithm")
+    resp[1].should.have.key("ChecksumAlgorithm").equals(["CRC32"])
+    resp[2].should.have.key("ChecksumAlgorithm").equals(["SHA256"])
 
 
 @mock_s3