diff --git a/themes/tiddlywiki/vanilla/base.tid b/themes/tiddlywiki/vanilla/base.tid
index ef774c7f9..2e8dd52ff 100644
--- a/themes/tiddlywiki/vanilla/base.tid
+++ b/themes/tiddlywiki/vanilla/base.tid
@@ -1468,6 +1468,7 @@ html body.tc-body.tc-single-tiddler-window {
 	right: 0;
 	bottom: 0;
 	left: 0;
+	z-index: 900;
 }
 
 .tc-modal-backdrop {