diff --git a/src/sourmash/index.py b/src/sourmash/index.py
index 443844c2b9..23b2d08f7d 100644
--- a/src/sourmash/index.py
+++ b/src/sourmash/index.py
@@ -1009,7 +1009,7 @@ def write_csv_header(cls, fp):
         w = csv.DictWriter(fp, fieldnames=cls.required_keys)
         w.writeheader()
 
-    def write_to_csv(self, fp, write_header=False):
+    def write_to_csv(self, fp, *, write_header=False):
         "write manifest CSV to specified file handle"
         w = csv.DictWriter(fp, fieldnames=self.required_keys)
 
diff --git a/src/sourmash/sourmash_args.py b/src/sourmash/sourmash_args.py
index b92e09aa71..b6d847116f 100644
--- a/src/sourmash/sourmash_args.py
+++ b/src/sourmash/sourmash_args.py
@@ -728,7 +728,7 @@ def close(self):
         manifest_name = f"SOURMASH-MANIFEST.csv"
 
         manifest_fp = StringIO()
-        manifest.write_to_csv(manifest_fp)
+        manifest.write_to_csv(manifest_fp, write_header=True)
         manifest_data = manifest_fp.getvalue().encode("utf-8")
 
         self.storage.save(manifest_name, manifest_data, overwrite=True)