diff --git a/src/calibre/srv/render_book.py b/src/calibre/srv/render_book.py
index 6756b64c9d..e5fe1d9095 100644
--- a/src/calibre/srv/render_book.py
+++ b/src/calibre/srv/render_book.py
@@ -239,8 +239,12 @@ class Container(ContainerBase):
         templ = '''
         <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
         <head><style>
-        html, body, img { height: 100%%; display: block; margin: 0; padding: 0; border-width: 0; }
-        img { width: auto; margin-left:auto; margin-right: auto; }
+        html, body, img { height: 100vh; display: block; margin: 0; padding: 0; border-width: 0; }
+        img {
+            width: auto; height: auto;
+            margin-left: auto; margin-right: auto;
+            max-width: 100vw; max-height: 100vh
+        }
         </style></head><body><img src="%s"/></body></html>
         '''
         if input_fmt == 'epub':
diff --git a/src/pyj/read_book/resources.pyj b/src/pyj/read_book/resources.pyj
index cea712acf1..b8dd57d52a 100644
--- a/src/pyj/read_book/resources.pyj
+++ b/src/pyj/read_book/resources.pyj
@@ -42,7 +42,7 @@ def load_resources(db, book, root_name, previous_resources, proceed):
     def got_one(data, name, mimetype):
         if False and name is book.manifest.title_page_name:
             # Enable to have cover image not preserve aspect ratio
-            data = data.replace('width: auto', 'width: 100%')
+            data = data.replace('width: auto; height: auto', 'width: 100vw; height: 100vh')
         ans[name] = v'[data, mimetype]'
         if jstype(data) is 'string':
             find_virtualized_resources(data)
