diff --git a/web/viewer.html b/web/viewer.html
index 4a307c7ef..360503006 100644
--- a/web/viewer.html
+++ b/web/viewer.html
@@ -2,6 +2,7 @@
 <html dir="ltr">
   <head>
     <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
     <title>PDF.js viewer</title>
     <!-- PDFJSSCRIPT_INCLUDE_FIREFOX_EXTENSION -->
 
