diff --git a/src/calibre/ebooks/conversion/plumber.py b/src/calibre/ebooks/conversion/plumber.py
index 3d345b50f3..7f38106229 100644
--- a/src/calibre/ebooks/conversion/plumber.py
+++ b/src/calibre/ebooks/conversion/plumber.py
@@ -368,7 +368,9 @@ OptionRecommendation(name='remove_paragraph_spacing_indent_size',
         recommended_value=1.5, level=OptionRecommendation.LOW,
         help=_('When calibre removes blank lines between paragraphs, it automatically '
             'sets a paragraph indent, to ensure that paragraphs can be easily '
-            'distinguished. This option controls the width of that indent (in em).')
+            'distinguished. This option controls the width of that indent (in em). '
+            'If you set this value to 0, then the indent specified in the input '
+            'document is used.')
         ),
 
 OptionRecommendation(name='prefer_metadata_cover',
diff --git a/src/calibre/ebooks/oeb/transforms/flatcss.py b/src/calibre/ebooks/oeb/transforms/flatcss.py
index 1493a647ae..078174218e 100644
--- a/src/calibre/ebooks/oeb/transforms/flatcss.py
+++ b/src/calibre/ebooks/oeb/transforms/flatcss.py
@@ -320,9 +320,10 @@ class CSSFlattener(object):
             if self.context.insert_blank_line:
                 cssdict['margin-top'] = cssdict['margin-bottom'] = \
                     '%fem'%self.context.insert_blank_line_size
-            if (self.context.remove_paragraph_spacing and
+            indent_size = self.context.remove_paragraph_spacing_indent_size
+            if (self.context.remove_paragraph_spacing and indent_size != 0.0 and
                 cssdict.get('text-align', None) not in ('center', 'right')):
-                cssdict['text-indent'] =  "%1.1fem" % self.context.remove_paragraph_spacing_indent_size
+                cssdict['text-indent'] =  "%1.1fem" % indent_size
 
         if cssdict:
             items = cssdict.items()