diff --git a/pyperf/_formatter.py b/pyperf/_formatter.py
index 6c3a1eea..131721d7 100644
--- a/pyperf/_formatter.py
+++ b/pyperf/_formatter.py
@@ -78,15 +78,8 @@ def format_number(number, unit=None, units=None):
             number = '10^%s' % pow10
 
     if isinstance(number, int) and number > 8192:
-        pow2 = 0
-        x = number
-        while x >= 2:
-            x, r = divmod(x, 2)
-            pow2 += 1
-            if r:
-                break
-        if not r:
-            number = '2^%s' % pow2
+        if number & (number-1) == 0:
+            number = '2^%s' % (number.bit_length() - 1)
 
     if not unit:
         return str(number)
diff --git a/pyperf/tests/test_utils.py b/pyperf/tests/test_utils.py
index edf8549c..24b4ec78 100644
--- a/pyperf/tests/test_utils.py
+++ b/pyperf/tests/test_utils.py
@@ -130,15 +130,15 @@ def test_format_number(self):
         self.assertEqual(format_number(33 * 10 ** 4, 'unit'),
                          '330000 units')
 
-        # powers of 10
+        # powers of 2
         self.assertEqual(format_number(2 ** 10, 'unit'),
                          '1024 units')
         self.assertEqual(format_number(2 ** 15, 'unit'),
                          '2^15 units')
         self.assertEqual(format_number(2 ** 15),
                          '2^15')
-        self.assertEqual(format_number(2 ** 10 + 1, 'unit'),
-                         '1025 units')
+        self.assertEqual(format_number(2 ** 15 - 1), '32767')
+        self.assertEqual(format_number(2 ** 15 + 1), '32769')
 
     def test_format_filesize(self):
         self.assertEqual(format_filesize(0),