diff --git a/src/calibre/ebooks/conversion/cli.py b/src/calibre/ebooks/conversion/cli.py
index 2ef633d0bb..62a941142b 100644
--- a/src/calibre/ebooks/conversion/cli.py
+++ b/src/calibre/ebooks/conversion/cli.py
@@ -137,7 +137,7 @@ def add_pipeline_options(parser, plumber):
                       'chapter', 'chapter_mark',
                       'prefer_metadata_cover', 'remove_first_image',
                       'insert_metadata', 'page_breaks_before',
-                      'preprocess_html',
+                      'preprocess_html', 'html_unwrap_factor',
                   ]
                   ),
 
diff --git a/src/calibre/ebooks/conversion/plumber.py b/src/calibre/ebooks/conversion/plumber.py
index 16282dd28d..3ea2926461 100644
--- a/src/calibre/ebooks/conversion/plumber.py
+++ b/src/calibre/ebooks/conversion/plumber.py
@@ -362,6 +362,15 @@ OptionRecommendation(name='preprocess_html',
             )
         ),
 
+OptionRecommendation(name='html_unwrap_factor',
+        recommended_value=0.40, level=OptionRecommendation.LOW,
+        help=_('Scale used to determine the length at which a line should '
+            'be unwrapped if preprocess is enabled. Valid values are a decimal between 0 and 1. The '
+            'default is 0.40, just below the median line length. This will unwrap typical books '
+            ' with hard line breaks, but should be reduced if the line length is variable.'
+            )
+        ),
+
 OptionRecommendation(name='smarten_punctuation',
         recommended_value=False, level=OptionRecommendation.LOW,
         help=_('Convert plain quotes, dashes and ellipsis to their '
diff --git a/src/calibre/ebooks/conversion/preprocess.py b/src/calibre/ebooks/conversion/preprocess.py
index 4538af96c4..e72e15c3d9 100644
--- a/src/calibre/ebooks/conversion/preprocess.py
+++ b/src/calibre/ebooks/conversion/preprocess.py
@@ -351,7 +351,7 @@ class HTMLPreProcessor(object):
                 # print "The pdf line length returned is " + str(length)
                 end_rules.append(
                     # Un wrap using punctuation
-                    (re.compile(r'(?<=.{%i}[a-z,;:)\-IA])\s*(?P<ital></(i|b|u)>)?\s*(<p.*?>\s*)+\s*(?=(<(i|b|u)>)?\s*[\w\d$(])' % length, re.UNICODE), wrap_lines),
+                    (re.compile(r'(?<=.{%i}([a-z,:)\-IA]|(?<!\&\w{4});))\s*(?P<ital></(i|b|u)>)?\s*(<p.*?>\s*)+\s*(?=(<(i|b|u)>)?\s*[\w\d$(])' % length, re.UNICODE), wrap_lines),
                 )
 
         for rule in self.PREPROCESS + start_rules:
diff --git a/src/calibre/ebooks/conversion/utils.py b/src/calibre/ebooks/conversion/utils.py
index 5301f70a16..3fe6ce0ed4 100644
--- a/src/calibre/ebooks/conversion/utils.py
+++ b/src/calibre/ebooks/conversion/utils.py
@@ -11,10 +11,11 @@ from calibre.utils.logging import default_log
 
 class PreProcessor(object):
 
-    def __init__(self, log=None):
+    def __init__(self, log=None, extra_opts=None):
         self.log = default_log if log is None else log
         self.html_preprocess_sections = 0
         self.found_indents = 0
+        self.extra_opts = extra_opts
 
     def chapter_head(self, match):
         chap = match.group('chap')
@@ -91,6 +92,7 @@ class PreProcessor(object):
         # If more than 40% of the lines are empty paragraphs then delete them to clean up spacing
         linereg = re.compile('(?<=<p).*?(?=</p>)', re.IGNORECASE|re.DOTALL)
         blankreg = re.compile(r'\s*<p[^>]*>\s*(<(b|i|u)>)?\s*(</(b|i|u)>)?\s*</p>', re.IGNORECASE)
+        #multi_blank = re.compile(r'(\s*<p[^>]*>\s*(<(b|i|u)>)?\s*(</(b|i|u)>)?\s*</p>){2,}', re.IGNORECASE)
         blanklines = blankreg.findall(html)
         lines = linereg.findall(html)
         if len(lines) > 1:
@@ -147,15 +149,16 @@ class PreProcessor(object):
             format = 'html'
 
         # Calculate Length
-        length = line_length(format, html, 0.4)
+        length = line_length('pdf', html, getattr(self.extra_opts,
+            'html_unwrap_factor', 0.4))
         self.log("*** Median line length is " + str(length) + ",calculated with " + format + " format ***")
         #
         # Unwrap and/or delete soft-hyphens, hyphens
         html = re.sub(u'­\s*(</span>\s*(</[iubp]>\s*<[iubp][^>]*>\s*)?<span[^>]*>|</[iubp]>\s*<[iubp][^>]*>)?\s*', '', html)
         html = re.sub(u'(?<=[-–—])\s*(?=<)(</span>\s*(</[iubp]>\s*<[iubp][^>]*>\s*)?<span[^>]*>|</[iubp]>\s*<[iubp][^>]*>)?\s*(?=[[a-z\d])', '', html)
 
-        # Unwrap lines using punctation if the median length of all lines is less than 200
-        unwrap = re.compile(r"(?<=.{%i}[a-z,;:\IA])\s*</(span|p|div)>\s*(</(p|span|div)>)?\s*(?P<up2threeblanks><(p|span|div)[^>]*>\s*(<(p|span|div)[^>]*>\s*</(span|p|div)>\s*)</(span|p|div)>\s*){0,3}\s*<(span|div|p)[^>]*>\s*(<(span|div|p)[^>]*>)?\s*" % length, re.UNICODE)
+        # Unwrap lines using punctation and line length
+        unwrap = re.compile(r"(?<=.{%i}([a-z,;):\IA]|(?<!\&\w{4});))\s*</(span|p|div)>\s*(</(p|span|div)>)?\s*(?P<up2threeblanks><(p|span|div)[^>]*>\s*(<(p|span|div)[^>]*>\s*</(span|p|div)>\s*)</(span|p|div)>\s*){0,3}\s*<(span|div|p)[^>]*>\s*(<(span|div|p)[^>]*>)?\s*" % length, re.UNICODE)
         html = unwrap.sub(' ', html)
 
         # If still no sections after unwrapping mark split points on lines with no punctuation
diff --git a/src/calibre/ebooks/lrf/input.py b/src/calibre/ebooks/lrf/input.py
index 1d730ab573..c54f3b071f 100644
--- a/src/calibre/ebooks/lrf/input.py
+++ b/src/calibre/ebooks/lrf/input.py
@@ -12,6 +12,7 @@ from copy import deepcopy
 from lxml import etree
 
 from calibre.customize.conversion import InputFormatPlugin
+from calibre.ebooks.conversion.utils import PreProcessor
 from calibre import guess_type
 
 class Canvas(etree.XSLTExtension):
@@ -419,4 +420,9 @@ class LRFInput(InputFormatPlugin):
         styles.write()
         return os.path.abspath('content.opf')
 
+    def preprocess_html(self, html):
+        preprocessor = PreProcessor(log=getattr(self, 'log', None))
+        return preprocessor(html)
+
+
 
diff --git a/src/calibre/gui2/convert/structure_detection.py b/src/calibre/gui2/convert/structure_detection.py
index f2ca49d1bd..3f350d4508 100644
--- a/src/calibre/gui2/convert/structure_detection.py
+++ b/src/calibre/gui2/convert/structure_detection.py
@@ -26,8 +26,10 @@ class StructureDetectionWidget(Widget, Ui_Form):
                 'remove_first_image',
                 'insert_metadata', 'page_breaks_before',
                 'preprocess_html', 'remove_header', 'header_regex',
-                'remove_footer', 'footer_regex']
+                'remove_footer', 'footer_regex','html_unwrap_factor']
                 )
+        self.opt_html_unwrap_factor.setEnabled(False)
+        self.huf_label.setEnabled(False)
         self.db, self.book_id = db, book_id
         for x in ('pagebreak', 'rule', 'both', 'none'):
             self.opt_chapter_mark.addItem(x)
@@ -64,3 +66,8 @@ class StructureDetectionWidget(Widget, Ui_Form):
                 _('The XPath expression %s is invalid.')%x.text).exec_()
                 return False
         return True
+
+    def set_value_handler(self, g, val):
+        if val is None and g is self.opt_html_unwrap_factor:
+            g.setValue(0.0)
+            return True
diff --git a/src/calibre/gui2/convert/structure_detection.ui b/src/calibre/gui2/convert/structure_detection.ui
index c0b3de3bd9..21fe365e99 100644
--- a/src/calibre/gui2/convert/structure_detection.ui
+++ b/src/calibre/gui2/convert/structure_detection.ui
@@ -14,10 +14,10 @@
    <string>Form</string>
   </property>
   <layout class="QGridLayout" name="gridLayout">
-   <item row="0" column="0" colspan="2">
+   <item row="0" column="1" colspan="2">
     <widget class="XPathEdit" name="opt_chapter" native="true"/>
    </item>
-   <item row="1" column="0">
+   <item row="1" column="0" colspan="2">
     <widget class="QLabel" name="label">
      <property name="text">
       <string>Chapter &amp;mark:</string>
@@ -27,31 +27,31 @@
      </property>
     </widget>
    </item>
-   <item row="1" column="1">
+   <item row="1" column="2">
     <widget class="QComboBox" name="opt_chapter_mark">
      <property name="minimumContentsLength">
       <number>20</number>
      </property>
     </widget>
    </item>
-   <item row="2" column="0">
+   <item row="2" column="0" colspan="2">
     <widget class="QCheckBox" name="opt_remove_first_image">
      <property name="text">
       <string>Remove first &amp;image</string>
      </property>
     </widget>
    </item>
-   <item row="4" column="0">
+   <item row="5" column="0" colspan="2">
     <widget class="QCheckBox" name="opt_insert_metadata">
      <property name="text">
       <string>Insert &amp;metadata as page at start of book</string>
      </property>
     </widget>
    </item>
-   <item row="10" column="0" colspan="2">
+   <item row="11" column="0" colspan="3">
     <widget class="XPathEdit" name="opt_page_breaks_before" native="true"/>
    </item>
-   <item row="11" column="0" colspan="2">
+   <item row="12" column="0" colspan="3">
     <spacer name="verticalSpacer">
      <property name="orientation">
       <enum>Qt::Vertical</enum>
@@ -64,27 +64,66 @@
      </property>
     </spacer>
    </item>
-   <item row="7" column="0">
+   <item row="8" column="0" colspan="2">
     <widget class="QCheckBox" name="opt_remove_footer">
      <property name="text">
       <string>Remove F&amp;ooter</string>
      </property>
     </widget>
    </item>
-   <item row="5" column="0">
+   <item row="6" column="0" colspan="2">
     <widget class="QCheckBox" name="opt_remove_header">
      <property name="text">
       <string>Remove H&amp;eader</string>
      </property>
     </widget>
    </item>
-   <item row="6" column="0" colspan="2">
+   <item row="7" column="0" colspan="3">
     <widget class="RegexEdit" name="opt_header_regex" native="true"/>
    </item>
-   <item row="8" column="0" colspan="2">
+   <item row="9" column="0" colspan="3">
     <widget class="RegexEdit" name="opt_footer_regex" native="true"/>
    </item>
-   <item row="3" column="0">
+   <item row="4" column="1">
+    <widget class="QLabel" name="huf_label">
+     <property name="text">
+      <string>Line &amp;un-wrap factor during preprocess:</string>
+     </property>
+     <property name="buddy">
+      <cstring>opt_html_unwrap_factor</cstring>
+     </property>
+    </widget>
+   </item>
+   <item row="4" column="2">
+    <widget class="QDoubleSpinBox" name="opt_html_unwrap_factor">
+     <property name="toolTip">
+      <string/>
+     </property>
+     <property name="maximum">
+      <double>1.000000000000000</double>
+     </property>
+     <property name="singleStep">
+      <double>0.050000000000000</double>
+     </property>
+     <property name="value">
+      <double>0.400000000000000</double>
+     </property>
+    </widget>
+   </item>
+   <item row="4" column="0">
+    <spacer name="horizontalSpacer">
+     <property name="orientation">
+      <enum>Qt::Horizontal</enum>
+     </property>
+     <property name="sizeHint" stdset="0">
+      <size>
+       <width>40</width>
+       <height>20</height>
+      </size>
+     </property>
+    </spacer>
+   </item>
+   <item row="3" column="0" colspan="2">
     <widget class="QCheckBox" name="opt_preprocess_html">
      <property name="text">
       <string>&amp;Preprocess input file to possibly improve structure detection</string>
@@ -108,5 +147,38 @@
   </customwidget>
  </customwidgets>
  <resources/>
- <connections/>
+ <connections>
+  <connection>
+   <sender>opt_preprocess_html</sender>
+   <signal>toggled(bool)</signal>
+   <receiver>opt_html_unwrap_factor</receiver>
+   <slot>setEnabled(bool)</slot>
+   <hints>
+    <hint type="sourcelabel">
+     <x>328</x>
+     <y>87</y>
+    </hint>
+    <hint type="destinationlabel">
+     <x>481</x>
+     <y>113</y>
+    </hint>
+   </hints>
+  </connection>
+  <connection>
+   <sender>opt_preprocess_html</sender>
+   <signal>toggled(bool)</signal>
+   <receiver>huf_label</receiver>
+   <slot>setEnabled(bool)</slot>
+   <hints>
+    <hint type="sourcelabel">
+     <x>295</x>
+     <y>88</y>
+    </hint>
+    <hint type="destinationlabel">
+     <x>291</x>
+     <y>105</y>
+    </hint>
+   </hints>
+  </connection>
+ </connections>
 </ui>