diff --git a/src/utils/ansi.py b/src/utils/ansi.py
index 72b6f8006..84d7a7f54 100644
--- a/src/utils/ansi.py
+++ b/src/utils/ansi.py
@@ -356,7 +356,7 @@ def _spacing_preflight(func):
     def wrapped(self, width, fillchar=None):
         if fillchar is None:
             fillchar = " "
-        if (len(fillchar) != 1) or (not isinstance(fillchar, str)):
+        if (len(fillchar) != 1) or (not isinstance(fillchar, basestring)):
             raise TypeError("must be char, not %s" % type(fillchar))
         if not isinstance(width, int):
             raise TypeError("integer argument expected, got %s" % type(width))