diff --git a/src/calibre/library/catalogs/bibtex.py b/src/calibre/library/catalogs/bibtex.py
index d21d9a6fa7..445e2e24c0 100644
--- a/src/calibre/library/catalogs/bibtex.py
+++ b/src/calibre/library/catalogs/bibtex.py
@@ -14,7 +14,7 @@ from calibre.library.catalogs import FIELDS, TEMPLATE_ALLOWED_FIELDS
 from calibre.customize.conversion import DummyReporter
 from calibre.constants import preferred_encoding
 from calibre.ebooks.metadata import format_isbn
-from polyglot.builtins import string_or_bytes, unicode_type
+from polyglot.builtins import string_or_bytes
 
 
 class BIBTEX(CatalogPlugin):
@@ -350,7 +350,7 @@ class BIBTEX(CatalogPlugin):
             bibtexc.ascii_bibtex = True
 
         # Check citation choice and go to default in case of bad CLI
-        if isinstance(opts.impcit, (str, unicode_type)) :
+        if isinstance(opts.impcit, string_or_bytes) :
             if opts.impcit == 'False' :
                 citation_bibtex= False
             elif opts.impcit == 'True' :
@@ -362,7 +362,7 @@ class BIBTEX(CatalogPlugin):
             citation_bibtex= opts.impcit
 
         # Check add file entry and go to default in case of bad CLI
-        if isinstance(opts.addfiles, (StringType, UnicodeType)) :
+        if isinstance(opts.addfiles, string_or_bytes) :
             if opts.addfiles == 'False' :
                 addfiles_bibtex = False
             elif opts.addfiles == 'True' :
diff --git a/src/calibre/srv/http_response.py b/src/calibre/srv/http_response.py
index 8313d18e32..c1b5547bf5 100644
--- a/src/calibre/srv/http_response.py
+++ b/src/calibre/srv/http_response.py
@@ -30,6 +30,8 @@ from polyglot import http_client, reprlib
 
 Range = namedtuple('Range', 'start stop size')
 MULTIPART_SEPARATOR = uuid.uuid4().hex
+if isinstance(MULTIPART_SEPARATOR, bytes):
+    MULTIPART_SEPARATOR = MULTIPART_SEPARATOR.decode('ascii')
 COMPRESSIBLE_TYPES = {'application/json', 'application/javascript', 'application/xml', 'application/oebps-package+xml'}
 if is_py3:
     import zlib
@@ -450,7 +452,10 @@ class HTTPConnection(HTTPRequest):
 
     def send_range_not_satisfiable(self, content_length):
         buf = [
-            '%s %d %s' % (self.response_protocol, http_client.REQUESTED_RANGE_NOT_SATISFIABLE, http_client.responses[http_client.REQUESTED_RANGE_NOT_SATISFIABLE]),
+            '%s %d %s' % (
+                self.response_protocol,
+                http_client.REQUESTED_RANGE_NOT_SATISFIABLE,
+                http_client.responses[http_client.REQUESTED_RANGE_NOT_SATISFIABLE]),
             "Date: " + http_date(),
             "Content-Range: bytes */%d" % content_length,
         ]
diff --git a/src/calibre/utils/unrar.py b/src/calibre/utils/unrar.py
index fc6a767843..a11ad5fc9e 100644
--- a/src/calibre/utils/unrar.py
+++ b/src/calibre/utils/unrar.py
@@ -127,8 +127,9 @@ def test_basic():
 
     def do_test(stream):
         c = comment(stream)
-        if c != 'some comment\n':
-            raise ValueError('Comment not read: %r != %r' % (c, b'some comment\n'))
+        expected = 'some comment\n'
+        if c != expected:
+            raise ValueError('Comment not read: %r != %r' % (c, expected))
         if set(names(stream)) != {
             '1/sub-one', 'one.txt', '2/sub-two.txt', '诶比屁.txt', 'Füße.txt',
             'uncompressed', 'max-compressed'}: