diff --git a/src/calibre/ebooks/pdf/render/fonts.py b/src/calibre/ebooks/pdf/render/fonts.py
index c5011a8822..48b48fe919 100644
--- a/src/calibre/ebooks/pdf/render/fonts.py
+++ b/src/calibre/ebooks/pdf/render/fonts.py
@@ -181,8 +181,12 @@ class Font(object):
             self.metrics.sfnt(self.font_stream)
 
     def write_to_unicode(self, objects):
-        cmap = CMap(self.metrics.postscript_name, self.metrics.glyph_map,
-                    compress=self.compress)
+        try:
+            name = self.metrics.postscript_name
+        except KeyError:
+            from calibre.utils.short_uuid import uuid4
+            name = uuid4()
+        cmap = CMap(name, self.metrics.glyph_map, compress=self.compress)
         self.font_dict['ToUnicode'] = objects.add(cmap)
 
     def write_widths(self, objects):