Added missed calls of splitlist().
diff --git a/Lib/tkinter/font.py b/Lib/tkinter/font.py
index 4929241..2096093 100644
--- a/Lib/tkinter/font.py
+++ b/Lib/tkinter/font.py
@@ -81,7 +81,8 @@
         if exists:
             self.delete_font = False
             # confirm font exists
-            if self.name not in root.tk.call("font", "names"):
+            if self.name not in root.tk.splitlist(
+                    root.tk.call("font", "names")):
                 raise tkinter._tkinter.TclError(
                     "named font %s does not already exist" % (self.name,))
             # if font config info supplied, apply it