diff --git a/lib/matplotlib/font_manager.py b/lib/matplotlib/font_manager.py
index df954b691c58..239549e98657 100644
--- a/lib/matplotlib/font_manager.py
+++ b/lib/matplotlib/font_manager.py
@@ -93,11 +93,15 @@
     'ultra-expanded'  : 900}
 
 weight_dict = {
+    'hair'       :  50,
+    'thin'       :  50,
+    'extralight' : 100,
     'ultralight' : 100,
     'light'      : 200,
     'normal'     : 400,
     'regular'    : 400,
     'book'       : 400,
+    'plain'      : 400,
     'medium'     : 500,
     'roman'      : 500,
     'semibold'   : 600,
@@ -105,7 +109,9 @@
     'demi'       : 600,
     'bold'       : 700,
     'heavy'      : 800,
+    'extrabold'  : 800,
     'extra bold' : 800,
+    'ultrabold'  : 800,
     'black'      : 900}
 
 font_family_aliases = {
@@ -402,6 +408,7 @@ def ttfFontProperty(font):
     *font* is a :class:`FT2Font` instance.
     """
     name = font.family_name
+    style_name = font.style_name.lower().strip()
 
     #  Styles are: italic, oblique, and normal (default)
 
@@ -437,10 +444,14 @@ def ttfFontProperty(font):
 
     weight = next((w for w in weight_dict if sfnt4.find(w) >= 0), None)
     if not weight:
-        if font.style_flags & ft2font.BOLD:
-            weight = 700
-        else:
+        weight = next((w for w in weight_dict if style_name.find(w) >= 0), None)
+        if weight:
+            pass
+        elif style_name in ["italic", "oblique", "condensed"]:
             weight = 400
+        else:
+            # give up rather than risk making mistakes (reason: #8550)
+            raise KeyError("unknown weight: {!r}".format(font.family_name))
 
     #  Stretch can be absolute and relative
     #  Absolute stretches are: ultra-condensed, extra-condensed, condensed,