diff --git a/src/calibre/ebooks/pdf/html_writer.py b/src/calibre/ebooks/pdf/html_writer.py
index da8bff51d6..8d16d0addb 100644
--- a/src/calibre/ebooks/pdf/html_writer.py
+++ b/src/calibre/ebooks/pdf/html_writer.py
@@ -980,7 +980,7 @@ def add_header_footer(manager, opts, pdf_doc, container, page_number_display_map
             'page-break-after': 'always',
             'display': 'flex',
             'flex-direction': 'column',
-            'height': '100%',
+            'height': '100vh',
             'justify-content': justify,
             'margin-left': '{}pt'.format(margins.left),
             'margin-right': '{}pt'.format(margins.right),