diff -r 913268337886 Lib/fractions.py
--- a/Lib/fractions.py	Sun Aug 21 17:41:56 2016 +1000
+++ b/Lib/fractions.py	Sun Aug 21 09:45:43 2016 +0100
@@ -484,10 +484,14 @@
                     return Fraction(a._numerator ** power,
                                     a._denominator ** power,
                                     _normalize=False)
-                else:
+                elif a._numerator >= 0:
                     return Fraction(a._denominator ** -power,
                                     a._numerator ** -power,
                                     _normalize=False)
+                else:
+                    return Fraction((-a._denominator) ** -power,
+                                    (-a._numerator) ** -power,
+                                    _normalize=False)
             else:
                 # A fractional power will generally produce an
                 # irrational number.
diff -r 913268337886 Lib/test/test_fractions.py
--- a/Lib/test/test_fractions.py	Sun Aug 21 17:41:56 2016 +1000
+++ b/Lib/test/test_fractions.py	Sun Aug 21 09:45:43 2016 +0100
@@ -356,6 +356,19 @@
         z = pow(F(-1), F(1, 2))
         self.assertAlmostEqual(z.real, 0)
         self.assertEqual(z.imag, 1)
+        # Regression test for #27539.
+        p = F(-1, 2) ** 0
+        self.assertEqual(p, F(1, 1))
+        self.assertEqual(p.numerator, 1)
+        self.assertEqual(p.denominator, 1)
+        p = F(-1, 2) ** -1
+        self.assertEqual(p, F(-2, 1))
+        self.assertEqual(p.numerator, -2)
+        self.assertEqual(p.denominator, 1)
+        p = F(-1, 2) ** -2
+        self.assertEqual(p, F(4, 1))
+        self.assertEqual(p.numerator, 4)
+        self.assertEqual(p.denominator, 1)
 
     def testMixedArithmetic(self):
         self.assertTypedEquals(F(11, 10), F(1, 10) + 1)