diff --git a/pyperf/_formatter.py b/pyperf/_formatter.py
index 11b40bc5..6c3a1eea 100644
--- a/pyperf/_formatter.py
+++ b/pyperf/_formatter.py
@@ -32,7 +32,7 @@ def format_filesize(size):
     if size > 10 * 1024 * 1024:
         return '%.1f MiB' % (size / (1024.0 * 1024.0))
 
-    return '%.1f kiB' % (size / 1024.0)
+    return '%.1f KiB' % (size / 1024.0)
 
 
 def format_filesizes(sizes):
diff --git a/pyperf/tests/test_perf_cli.py b/pyperf/tests/test_perf_cli.py
index d5ed5890..6423c52b 100644
--- a/pyperf/tests/test_perf_cli.py
+++ b/pyperf/tests/test_perf_cli.py
@@ -556,13 +556,13 @@ def test_dump(self):
     def test_dump_track_memory(self):
         expected = """
             Run 1: calibrate the number of loops: 2^15
-            - calibrate 1: 7188.0 kiB (loops: 2^15)
+            - calibrate 1: 7188.0 KiB (loops: 2^15)
             Run 2: 0 warmups, 1 value, 2^15 loops
-            - value 1: 7188.0 kiB
+            - value 1: 7188.0 KiB
             Run 3: 0 warmups, 1 value, 2^15 loops
-            - value 1: 7192.0 kiB
+            - value 1: 7192.0 KiB
             Run 4: 0 warmups, 1 value, 2^15 loops
-            - value 1: 7208.0 kiB
+            - value 1: 7208.0 KiB
         """
         filename = os.path.join(TESTDIR, 'track_memory.json')
         stdout = self.run_command('dump', filename)
diff --git a/pyperf/tests/test_utils.py b/pyperf/tests/test_utils.py
index 3aeffe64..edf8549c 100644
--- a/pyperf/tests/test_utils.py
+++ b/pyperf/tests/test_utils.py
@@ -146,7 +146,7 @@ def test_format_filesize(self):
         self.assertEqual(format_filesize(1),
                          '1 byte')
         self.assertEqual(format_filesize(10 * 1024),
-                         '10.0 kiB')
+                         '10.0 KiB')
         self.assertEqual(format_filesize(12.4 * 1024 * 1024),
                          '12.4 MiB')