diff --git a/src/calibre/ebooks/html.py b/src/calibre/ebooks/html.py
index 84af7527bd..f2338ffdff 100644
--- a/src/calibre/ebooks/html.py
+++ b/src/calibre/ebooks/html.py
@@ -796,7 +796,17 @@ class Processor(Parser):
                 setting = ''
             face = font.attrib.pop('face', None)
             if face is not None:
-                setting += 'font-face:%s;'%face
+                faces = []
+                for face in face.split(','):
+                    if ' ' in face:
+                        face = "%s" % face
+                    faces.append(face)
+                for generic in ('serif', 'sans-serif', 'monospace'):
+                    if generic in faces:
+                        break
+                else:
+                    faces.append('serif')
+                setting += 'font-family:%s;'% ', '.join(faces)
             color = font.attrib.pop('color', None)
             if color is not None:
                 setting += 'color:%s'%color
diff --git a/src/calibre/ebooks/oeb/profile.py b/src/calibre/ebooks/oeb/profile.py
index 3fdec6c8a5..3ecb0c5fca 100644
--- a/src/calibre/ebooks/oeb/profile.py
+++ b/src/calibre/ebooks/oeb/profile.py
@@ -42,7 +42,7 @@ PROFILES = {
     # Not really, but let's pretend
     'MobiDesktop':
         Profile(width=280, height=300, dpi=96, fbase=18,
-                fsizes=[14, 14, 16, 18, 20, 22, 22, 24]),
+                fsizes=[14, 14, 16, 18, 20, 22, 24, 26]),
     
     # No clue on usable screen size and DPI
     'CybookG3':
diff --git a/src/calibre/ebooks/oeb/transforms/flatcss.py b/src/calibre/ebooks/oeb/transforms/flatcss.py
index 2e6e64cdfa..5ad9042c7b 100644
--- a/src/calibre/ebooks/oeb/transforms/flatcss.py
+++ b/src/calibre/ebooks/oeb/transforms/flatcss.py
@@ -33,12 +33,13 @@ class KeyMapper(object):
     def relate(size, base):
         size = float(size)
         base = float(base)
-        if size == base: return 0
+        if abs(size - base) < 0.1: return 0
         sign = -1 if size < base else 1
         endp = 0 if size < base else 36
         diff = (abs(base - size) * 3) + ((36 - size) / 100)
         logb = abs(base - endp) 
-        return sign * math.log(diff, logb)
+        result = sign * math.log(diff, logb)
+        return result
         
     def __getitem__(self, ssize):
         if ssize in self.cache:
@@ -122,6 +123,8 @@ class CSSFlattener(object):
             fsize = self.context.source.fbase
             self.baseline_node(body, stylizer, sizes, fsize)
         sbase = max(sizes.items(), key=operator.itemgetter(1))[0]
+        self.oeb.logger.info(
+            "Source base font size is %0.05fpt" % sbase)
         return sbase
 
     def clean_edges(self, cssdict, style, fsize):
@@ -154,14 +157,14 @@ class CSSFlattener(object):
         if node.tag == XHTML('font'):
             node.tag = XHTML('span')
             if 'size' in node.attrib:
-                size = node.attrib['size']
-                if size.startswith('+'):
-                    cssdict['font-size'] = 'larger'
-                elif size.startswith('-'):
-                    cssdict['font-size'] = 'smaller'
-                else:
+                size = node.attrib['size'].strip()
+                if size:
                     fnums = self.context.source.fnums
-                    cssdict['font-size'] = fnums[int(size)]
+                    if size[0] in ('+', '-'):
+                        # Oh, the warcrimes
+                        cssdict['font-size'] = fnums[3+int(size)]
+                    else:
+                        cssdict['font-size'] = fnums[int(size)]
                 del node.attrib['size']
         if 'color' in node.attrib:
             cssdict['color'] = node.attrib['color']