diff --git a/src/calibre/gui2/tweak_book/preview.py b/src/calibre/gui2/tweak_book/preview.py
index 5c236ca050..7964e53900 100644
--- a/src/calibre/gui2/tweak_book/preview.py
+++ b/src/calibre/gui2/tweak_book/preview.py
@@ -20,7 +20,8 @@ from threading import Thread
 
 from calibre import prints
 from calibre.constants import (
-    FAKE_HOST, FAKE_PROTOCOL, __version__, is_running_from_develop
+    FAKE_HOST, FAKE_PROTOCOL, __version__, is_running_from_develop, ismacos,
+    iswindows
 )
 from calibre.ebooks.oeb.base import OEB_DOCS, XHTML_MIME, serialize
 from calibre.ebooks.oeb.polish.parsing import parse
@@ -252,6 +253,7 @@ def get_editor_settings(tprefs):
         'bg': get_color('preview_background', dark_color),
         'fg': get_color('preview_foreground', dark_text_color),
         'link': get_color('preview_link_color', dark_link_color),
+        'os': 'windows' if iswindows else ('macos' if ismacos else 'linux'),
     }
 
 
diff --git a/src/pyj/editor.pyj b/src/pyj/editor.pyj
index 6be92a4a3e..95e1c7fc0a 100644
--- a/src/pyj/editor.pyj
+++ b/src/pyj/editor.pyj
@@ -208,11 +208,13 @@ def load_mathjax():
 
 
 if document.body:
+    settings = JSON.parse(window.navigator.userAgent.split('|')[1])
+    css = '[data-in-split-mode="1"] [data-is-block="1"]:hover { cursor: pointer !important; border-top: solid 5px green !important }'
+    if settings.os is 'macos':
+        # See settings.pyj for reason for webkit-hyphenate-character
+        css += '\n* { -webkit-hyphenate-character: "-" !important }\n'
     document.body.addEventListener('click', onclick, True)
-    document.documentElement.appendChild(E.style(
-        type='text/css',
-        '[data-in-split-mode="1"] [data-is-block="1"]:hover { cursor: pointer !important; border-top: solid 5px green !important }'
-    ))
+    document.documentElement.appendChild(E.style(type='text/css', css))
 
     fix_fullscreen_svg_images()
     if check_for_maths():