diff --git a/src/calibre/ebooks/txt/processor.py b/src/calibre/ebooks/txt/processor.py
index 22ace69037..6a20703cbb 100644
--- a/src/calibre/ebooks/txt/processor.py
+++ b/src/calibre/ebooks/txt/processor.py
@@ -37,8 +37,8 @@ def clean_txt(txt):
     txt = re.sub('[ ]{2,}', ' ', txt)
 
     # Remove blank space from the beginning and end of the document.
-    txt = re.sub('^\s+(?=.)', '', txt)
-    txt = re.sub('(?<=.)\s+$', '', txt)
+    txt = re.sub(r'^\s+(?=.)', '', txt)
+    txt = re.sub(r'(?<=.)\s+$', '', txt)
     # Remove excessive line breaks.
     txt = re.sub('\n{5,}', '\n\n\n\n', txt)
     # remove ASCII invalid chars : 0 to 8 and 11-14 to 24
@@ -178,7 +178,7 @@ def separate_hard_scene_breaks(txt):
             return '\n%s\n' % line
         else:
             return line
-    txt = re.sub(u'(?miu)^[ \t-=~\/_]+$', lambda mo: sep_break(mo.group()), txt)
+    txt = re.sub(type(u'')(r'(?miu)^[ \t-=~\/_]+$'), lambda mo: sep_break(mo.group()), txt)
     return txt
 
 
@@ -216,7 +216,7 @@ def split_string_separator(txt, size):
     Splits the text by putting \n\n at the point size.
     '''
     if len(txt) > size:
-        txt = ''.join([re.sub(u'\.(?P<ends>[^.]*)$', '.\n\n\g<ends>',
+        txt = ''.join([re.sub(type(u'')(r'\.(?P<ends>[^.]*)$'), r'.\n\n\g<ends>',
             txt[i:i+size], 1) for i in
             xrange(0, len(txt), size)])
     return txt
@@ -236,7 +236,7 @@ def detect_paragraph_type(txt):
     '''
     txt = txt.replace('\r\n', '\n')
     txt = txt.replace('\r', '\n')
-    txt_line_count = len(re.findall('(?mu)^\s*.+$', txt))
+    txt_line_count = len(re.findall(r'(?mu)^\s*.+$', txt))
 
     # Check for hard line breaks - true if 55% of the doc breaks in the same region
     docanalysis = DocAnalysis('txt', txt)
@@ -244,11 +244,11 @@ def detect_paragraph_type(txt):
 
     if hardbreaks:
         # Determine print percentage
-        tab_line_count = len(re.findall('(?mu)^(\t|\s{2,}).+$', txt))
+        tab_line_count = len(re.findall(r'(?mu)^(\t|\s{2,}).+$', txt))
         print_percent = tab_line_count / float(txt_line_count)
 
         # Determine block percentage
-        empty_line_count = len(re.findall('(?mu)^\s*$', txt))
+        empty_line_count = len(re.findall(r'(?mu)^\s*$', txt))
         block_percent = empty_line_count / float(txt_line_count)
 
         # Compare the two types - the type with the larger number of instances wins
@@ -286,9 +286,9 @@ def detect_formatting_type(txt):
     markdown_count += len(re.findall('(?mu)^=+$', txt))
     markdown_count += len(re.findall('(?mu)^-+$', txt))
     # Images
-    markdown_count += len(re.findall('(?u)!\[.*?\](\[|\()', txt))
+    markdown_count += len(re.findall(r'(?u)!\[.*?\](\[|\()', txt))
     # Links
-    markdown_count += len(re.findall('(?u)^|[^!]\[.*?\](\[|\()', txt))
+    markdown_count += len(re.findall(r'(?u)^|[^!]\[.*?\](\[|\()', txt))
 
     # Check for textile
     # Headings