diff --git a/mercurial/patch.py b/mercurial/patch.py
--- a/mercurial/patch.py
+++ b/mercurial/patch.py
@@ -2492,9 +2492,9 @@
         chompline = line.rstrip('\n')
         # highlight tabs and trailing whitespace
         stripline = chompline.rstrip()
-        if line[0] == '-':
+        if line[0:1] == '-':
             label = 'diff.deleted'
-        elif line[0] == '+':
+        elif line[0:1] == '+':
             label = 'diff.inserted'
         else:
             raise error.ProgrammingError('unexpected hunk line: %s' % line)
@@ -2515,9 +2515,9 @@
     a = ''
     b = ''
     for line in hunklines:
-        if line[0] == '-':
+        if line[0:1] == '-':
             a += line[1:]
-        elif line[0] == '+':
+        elif line[0:1] == '+':
             b += line[1:]
         else:
             raise error.ProgrammingError('unexpected hunk line: %s' % line)