diff --git a/src/calibre/ebooks/pdf/render/from_html.py b/src/calibre/ebooks/pdf/render/from_html.py
index 53c1341cb4..01aa178d7e 100644
--- a/src/calibre/ebooks/pdf/render/from_html.py
+++ b/src/calibre/ebooks/pdf/render/from_html.py
@@ -390,10 +390,10 @@ class PDFWriter(QObject):
         if self.paged_js is None:
             import uuid
             from calibre.utils.resources import compiled_coffeescript as cc
-            self.paged_js =  cc('ebooks.oeb.display.utils')
-            self.paged_js += cc('ebooks.oeb.display.indexing')
-            self.paged_js += cc('ebooks.oeb.display.paged')
-            self.paged_js += cc('ebooks.oeb.display.mathjax')
+            self.paged_js =  cc('ebooks.oeb.display.utils').decode('utf-8')
+            self.paged_js += cc('ebooks.oeb.display.indexing').decode('utf-8')
+            self.paged_js += cc('ebooks.oeb.display.paged').decode('utf-8')
+            self.paged_js += cc('ebooks.oeb.display.mathjax').decode('utf-8')
             if self.opts.pdf_hyphenate:
                 self.paged_js += P('viewer/hyphenate/Hyphenator.js', data=True).decode('utf-8')
                 hjs, self.hyphenate_lang = load_hyphenator_dicts({}, self.book_language)
diff --git a/src/calibre/gui2/toc/location.py b/src/calibre/gui2/toc/location.py
index f6fdd214bb..1ead67fa55 100644
--- a/src/calibre/gui2/toc/location.py
+++ b/src/calibre/gui2/toc/location.py
@@ -57,6 +57,8 @@ class Page(QWebPage):  # {{{
             from calibre.utils.resources import compiled_coffeescript
             self.js = compiled_coffeescript('ebooks.oeb.display.utils')
             self.js += compiled_coffeescript('ebooks.oeb.polish.choose')
+            if isinstance(self.js, bytes):
+                self.js = self.js.decode('utf-8')
         self.mainFrame().addToJavaScriptWindowObject("py_bridge", self)
         self.evaljs(self.js)
 # }}}
diff --git a/src/calibre/gui2/tweak_book/preview.py b/src/calibre/gui2/tweak_book/preview.py
index f66e58e9a1..c2e8633c86 100644
--- a/src/calibre/gui2/tweak_book/preview.py
+++ b/src/calibre/gui2/tweak_book/preview.py
@@ -286,6 +286,8 @@ class WebPage(QWebPage):
             self.js = compiled_coffeescript('ebooks.oeb.display.utils', dynamic=False)
             self.js += P('csscolorparser.js', data=True, allow_user_override=False)
             self.js += compiled_coffeescript('ebooks.oeb.polish.preview', dynamic=False)
+            if isinstance(self.js, bytes):
+                self.js = self.js.decode('utf-8')
         self._line_numbers = None
         mf = self.mainFrame()
         mf.addToJavaScriptWindowObject("py_bridge", self)