diff --git a/src/theme/book.js b/src/theme/book.js
index c2deb79c..df2c1251 100644
--- a/src/theme/book.js
+++ b/src/theme/book.js
@@ -372,7 +372,15 @@ function playpen_text(playpen) {
     });
 
     themePopup.addEventListener('focusout', function(e) {
-        if (!themePopup.contains(e.relatedTarget)) {
+        // e.relatedTarget is null in Safari and Firefox on macOS (see workaround below)
+        if (!!e.relatedTarget && !themePopup.contains(e.relatedTarget)) {
+            hideThemes();
+        }
+    });
+
+    // Should not be needed, but it works around an issue on macOS & iOS: https://github.com/rust-lang-nursery/mdBook/issues/628
+    document.addEventListener('click', function(e) {
+        if (themePopup.style.display === 'block' && !themeToggleButton.contains(e.target) && !themePopup.contains(e.target)) {
             hideThemes();
         }
     });