diff --git a/pandas/formats/css.py b/pandas/formats/css.py
index 40bc0156a1261..d9ad500b28fe6 100644
--- a/pandas/formats/css.py
+++ b/pandas/formats/css.py
@@ -163,8 +163,9 @@ def size_to_pt(self, val, em_pt=None, conversions=UNIT_RATIOS):
             try:
                 val = float(val)
             except ValueError:
-                warnings.warn('Unhandled font size: %r' % val + unit,
+                warnings.warn('Unhandled size: %r' % val + unit,
                               CSSWarning)
+                return self.size_to_pt('1!!default', conversions=conversions)
 
         while unit != 'pt':
             if unit == 'em':