diff --git a/setup/extensions.py b/setup/extensions.py
index 9a8a6e20a6..ebc258d7bd 100644
--- a/setup/extensions.py
+++ b/setup/extensions.py
@@ -257,6 +257,7 @@ if isunix:
     cc = os.environ.get('CC', 'gcc')
     cxx = os.environ.get('CXX', 'g++')
     cflags = os.environ.get('OVERRIDE_CFLAGS',
+        # '-Wall -DNDEBUG -ggdb -fno-strict-aliasing -pipe')
         '-O3 -Wall -DNDEBUG -fno-strict-aliasing -pipe')
     cflags = shlex.split(cflags) + ['-fPIC']
     ldflags = os.environ.get('OVERRIDE_LDFLAGS', '-Wall')
diff --git a/setup/sfntly.py b/setup/sfntly.py
index 79a25a53f0..298d0044f0 100644
--- a/setup/sfntly.py
+++ b/setup/sfntly.py
@@ -46,6 +46,7 @@ class SfntlyBuilderMixin(object):
             self.sfntly_cflags += [
                     '-D_UNICODE', '-DUNICODE',
             ] + shlex.split('/W4 /WX /Gm- /Gy /GR-')
+            self.cflags += ['-DWIN32']
         else:
             # Possibly add -fno-inline (slower, but more robust)
             self.sfntly_cflags += [
@@ -63,7 +64,10 @@ class SfntlyBuilderMixin(object):
             cflags.remove('/Ox')
         if '-O3' in cflags:
             cflags.remove('-O3')
-        cflags.insert(0, '/O2' if iswindows else '-O2')
+        if '/W3' in cflags:
+            cflags.remove('/W3')
+        if '-ggdb' not in cflags:
+            cflags.insert(0, '/O2' if iswindows else '-O2')
 
         groups = []
         all_headers = set()
@@ -71,7 +75,7 @@ class SfntlyBuilderMixin(object):
         src_dir = self.absolutize([os.path.join('sfntly', 'src')])[0]
         inc_dirs = [src_dir]
         self.inc_dirs += inc_dirs
-        inc_flags = builder.inc_dirs_to_cflags(inc_dirs)
+        inc_flags = builder.inc_dirs_to_cflags(self.inc_dirs)
         for loc in ('', 'port', 'data', 'math', 'table', 'table/bitmap',
                 'table/core', 'table/truetype'):
             path = os.path.join(src_dir, 'sfntly', *loc.split('/'))
diff --git a/src/calibre/utils/fonts/subset.py b/src/calibre/utils/fonts/subset.py
index 41f0365cdf..4fbadee955 100644
--- a/src/calibre/utils/fonts/subset.py
+++ b/src/calibre/utils/fonts/subset.py
@@ -10,6 +10,12 @@ __docformat__ = 'restructuredtext en'
 from future_builtins import map
 
 class NoGlyphs(ValueError):
+    'Raised when the font has no glyphs for the specified characters'
+    pass
+
+class UnsupportedFont(ValueError):
+    'Raised when the font is not supported for subsetting '
+    '(usually an OTF font with PostScript outlines).'
     pass
 
 def load_sfntly():
@@ -19,7 +25,7 @@ def load_sfntly():
         raise RuntimeError('Failed to load sfntly: %s'%err)
     return sfntly
 
-def subset(font_data, individual_chars, ranges):
+def subset(font_data, individual_chars, ranges=()):
     if font_data[:4] not in {b'\x00\x01\x00\x00', b'OTTO', b'true', b'typ1'}:
         raise ValueError('Not a supported font file. sfnt_version not recognized: %r'%
                 font_data[:4])
@@ -37,6 +43,8 @@ def subset(font_data, individual_chars, ranges):
     except sfntly.NoGlyphs:
         raise NoGlyphs('No glyphs were found in this font for the'
                 ' specified characters. Subsetting is pointless')
+    except sfntly.UnsupportedFont as e:
+        raise UnsupportedFont(type('')(e))
 
 def option_parser():
     import textwrap
@@ -99,6 +107,31 @@ def test():
     if len(sf) > 0.3 * len(raw):
         raise Exception('Subsetting failed')
 
+def all():
+    from calibre.utils.fonts.scanner import font_scanner
+    failed = []
+    for family in font_scanner.find_font_families():
+        for font in font_scanner.fonts_for_family(family):
+            raw = font_scanner.get_font_data(font)
+            print ('Subsetting', font['full_name'])
+            try:
+                sf, old_stats, new_stats = subset(raw, set(('a', 'b', 'c')), ())
+            except (NoGlyphs, UnsupportedFont) as e:
+                continue
+            except Exception as e:
+                print ('Failed!')
+                failed.append((font['full_name'], font['path'], unicode(e)))
+            else:
+                print ('Reduced to:', '%.1f'%(
+                        sum(new_stats.itervalues())/sum(old_stats.itervalues())
+                        * 100), '%')
+    if failed:
+        print ('\n\nFailures:')
+        for name, path, err in failed:
+            print (name, path, err)
+            print()
+
+
 def main(args):
     import sys, time
     from calibre import prints