Issue 3287: Raise correct exception for float inputs.
diff --git a/Lib/fractions.py b/Lib/fractions.py
index 3dc8184..944e1fc 100755
--- a/Lib/fractions.py
+++ b/Lib/fractions.py
@@ -96,9 +96,11 @@
 
         if denominator == 0:
             raise ZeroDivisionError('Fraction(%s, 0)' % numerator)
-
-        numerator = numerator.__index__()
-        denominator = denominator.__index__()
+        try:
+            numerator = numerator.__index__()
+            denominator = denominator.__index__()
+        except AttributeError:
+            raise TypeError('Numerator and denominator must support __index__.')
         g = gcd(numerator, denominator)
         self._numerator = numerator // g
         self._denominator = denominator // g