diff --git a/mercurial/hgweb/common.py b/mercurial/hgweb/common.py
--- a/mercurial/hgweb/common.py
+++ b/mercurial/hgweb/common.py
@@ -183,7 +183,7 @@
     try:
         os.stat(path)
         ct = pycompat.sysbytes(
-            mimetypes.guess_type(pycompat.fsdecode(path))[0] or "text/plain")
+            mimetypes.guess_type(pycompat.fsdecode(path))[0] or r"text/plain")
         with open(path, 'rb') as fh:
             data = fh.read()
 
diff --git a/mercurial/hgweb/webcommands.py b/mercurial/hgweb/webcommands.py
--- a/mercurial/hgweb/webcommands.py
+++ b/mercurial/hgweb/webcommands.py
@@ -151,7 +151,7 @@
     if stringutil.binary(text):
         mt = pycompat.sysbytes(
             mimetypes.guess_type(pycompat.fsdecode(f))[0]
-            or 'application/octet-stream')
+            or r'application/octet-stream')
         text = '(binary:%s)' % mt
 
     def lines(context):
@@ -864,7 +864,7 @@
         if f.isbinary():
             mt = pycompat.sysbytes(
                 mimetypes.guess_type(pycompat.fsdecode(f.path()))[0]
-                or 'application/octet-stream')
+                or r'application/octet-stream')
             return [_('(binary file %s, hash: %s)') % (mt, hex(f.filenode()))]
         return f.data().splitlines()
 
@@ -952,7 +952,7 @@
         if fctx.isbinary():
             mt = pycompat.sysbytes(
                 mimetypes.guess_type(pycompat.fsdecode(fctx.path()))[0]
-                or 'application/octet-stream')
+                or r'application/octet-stream')
             lines = [dagop.annotateline(fctx=fctx.filectx(fctx.filerev()),
                                         lineno=1, text='(binary:%s)' % mt)]
         else: