diff --git a/src/calibre/ebooks/pdf/reflow.py b/src/calibre/ebooks/pdf/reflow.py
index 815d7e12fa..fb0d882de7 100644
--- a/src/calibre/ebooks/pdf/reflow.py
+++ b/src/calibre/ebooks/pdf/reflow.py
@@ -243,17 +243,17 @@ class Text(Element):
         if self.font_size_em == other.font_size_em \
           and False \
           and self.font.id == other.font.id \
-          and re.match('<span style="font-size:', self.raw) is not None \
-          and re.match('<span style="font-size:', other.raw) is not None :
+          and re.match(r'<span style="font-size:', self.raw) is not None \
+          and re.match(r'<span style="font-size:', other.raw) is not None :
             # We have the same class, so merge
-            m_self = re.match('^(.+)</span>$', self.raw)
-            m_other = re.match('^<span style="font-size:.+em">(.+</span>)$', other.raw)
+            m_self = re.match(r'^(.+)</span>$', self.raw)
+            m_other = re.match(r'^<span style="font-size:.+em">(.+</span>)$', other.raw)
             if m_self and m_other:
                 self.raw = m_self.group(1)
                 other.raw = m_other.group(1)
         elif self.font_size_em != other.font_size_em \
           and self.font_size_em != 1.00 :
-            if re.match('<span', self.raw) is None :
+            if re.match(r'<span', self.raw) is None :
                 self.raw = '<span style="font-size:%sem">%s</span>'%(str(self.font_size_em),self.raw)
             # Try to allow for a very large initial character
             elif len(self.text_as_string) <= 2 \
@@ -263,7 +263,7 @@ class Text(Element):
                 # The line height gets set to the same as other parts of the file
                 # and the font size is reduced.
                 # These need to be fixed manually.
-                m_self = re.match('^(.+em">)(.+)$', self.raw)
+                m_self = re.match(r'^(.+em">)(.+)$', self.raw)
                 self.raw = m_self.group(1) \
                   + '<span style="float:left"><span style="line-height:0.5">' \
                   + m_self.group(2) + '</span></span>'
@@ -289,7 +289,7 @@ class Text(Element):
                     has_float = '<span style="float:right">'
                     has_gap = 1
                 #else leave has_gap
-            old_float = re.match('^(.*)(<span style="float:right">.*)</span>\s*$', self.raw)
+            old_float = re.match(r'^(.*)(<span style="float:right">.*)</span>\s*$', self.raw)
             if old_float:
                 # There is already a float as parts of a line are near the right.
                 # Remove the </span> and put it after this part
@@ -322,7 +322,7 @@ class Text(Element):
         # Note that the 2 parts could have different font sizes
         matchObj = re.match(r'^([^<]*)(<span[^>]*>)*(<a href[^>]+>)(.*)</a>(</span>)*(\s*)$', self.raw)
         if matchObj is not None :
-            otherObj = re.match('^([^<]*)(<span[^>]*>)*(<a href[^>]+>)(.*)(</a>)(</span>)*(.*)$', other.raw)
+            otherObj = re.match(r'^([^<]*)(<span[^>]*>)*(<a href[^>]+>)(.*)(</a>)(</span>)*(.*)$', other.raw)
             # There is another href, but is it for the same place?
             if otherObj is not None  and  matchObj.group(3) == otherObj.group(3) :
                 m2 = matchObj.group(2)
@@ -983,7 +983,7 @@ class Page:
             #
             # The left can wander by a few (SAME_INDENT) pixels.
             # "float:left" occurs where there is a multi-line character, so indentation is messed up
-            lchar = re.match('.*([^ ])\s*$', first_text.text_as_string)
+            lchar = re.match(r'.*([^ ])\s*$', first_text.text_as_string)
             last_char = ' '  # Nothing interesting
             if lchar is not None:
                 last_char = lchar.group(1)  # Final non-space char
@@ -1925,8 +1925,8 @@ class PDFDocument:
                         else:
                             merged_len = merged_text.right
                         # Allow where the last line ends with or next line starts with lower case.
-                        if re.match('.*[a-z, -]$', last_line.text_as_string) is not None \
-                          or re.match('^[a-z, -]', merged_text.text_as_string) is not None :
+                        if re.match(r'.*[a-z, -]$', last_line.text_as_string) is not None \
+                          or re.match(r'^[a-z, -]', merged_text.text_as_string) is not None :
                             merged_len = merged_text.right
 
                         # To use merged_len etc.
@@ -1936,8 +1936,8 @@ class PDFDocument:
                           and 'href=' not in merged_text.raw \
                           and merged_text.left < stats_left + merged_text.average_character_width \
                           and not last_spare > merged_len \
-                          and not (re.match('.*[.!?](\u201d|”)$', last_line.text_as_string) is not None
-                               and re.match('^(\u201c|“).*', merged_text.text_as_string) is not None):
+                          and not (re.match(r'.*[.!?](\u201d|”)$', last_line.text_as_string) is not None
+                               and re.match(r'^(\u201c|“).*', merged_text.text_as_string) is not None):
                             merge_done = True
                             # We don't want to merge partial pages
                             # i.e. if this is the last line, preserve its top/bottom till after merge
@@ -1970,7 +1970,7 @@ class PDFDocument:
                                 and (len(self.pages[pind+1].texts) == 0 \
                                  or self.pages[pind+1].texts[0].top > self.pages[pind+1].imgs[0].top)):
                                 page.page_break_after = True
-                    elif (re.match('.*[a-z, ]$', last_line.text_as_string) is not None \
+                    elif (re.match(r'.*[a-z, ]$', last_line.text_as_string) is not None \
                       or  last_line.final_width > page.width*self.opts.unwrap_factor):
                     #  or (last_line.right * 100.0 / page.right_margin) > LAST_LINE_PERCENT):
                         candidate = page