diff --git a/src/file/csv/SsBuilder.php b/src/file/csv/SsBuilder.php
index cab3717..85b83a3 100644
--- a/src/file/csv/SsBuilder.php
+++ b/src/file/csv/SsBuilder.php
@@ -50,9 +50,11 @@ class SsBuilder extends AbstractBuilder {
     }
     if ($ws === null) {
       $ws = $ss->createSheet()->setTitle($wsname);
+      $this->wroteHeaders = false;
     } else {
       $maxRow = wsutils::compute_max_coords($ws)[1];
       $this->nrow = $maxRow - 1;
+      $this->wroteHeaders = $maxRow > 1;
     }
     $this->ws = $ws;
   }