diff --git a/CHANGES.rst b/CHANGES.rst
index 7dc56b9e5..25463fe3c 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -21,11 +21,12 @@ Unreleased
 ----------
 
 - Greatly improved performance on PyPy, and other environments that need the
-  pure Python trace function.  Thanks, `Carl Friedrich Bolz-Tereick
-  <pull 1381_>`_.  Slightly improved performance when using the C trace
-  function, as most environments do.
+  pure Python trace function.  Thanks, Carl Friedrich Bolz-Tereick (`pull
+  1381`_ and `pull 1388`_).  Slightly improved performance when using the C
+  trace function, as most environments do.
 
 .. _pull 1381: https://github.com/nedbat/coveragepy/pull/1381
+.. _pull 1388: https://github.com/nedbat/coveragepy/pull/1388
 
 
 .. _changes_64:
diff --git a/coverage/pytracer.py b/coverage/pytracer.py
index 4389c9ed7..4f138074b 100644
--- a/coverage/pytracer.py
+++ b/coverage/pytracer.py
@@ -67,11 +67,10 @@ def __init__(self):
         # On exit, self.in_atexit = True
         atexit.register(setattr, self, 'in_atexit', True)
 
-        # cache a bound method on the instance, so that we don't have to
-        # re-create a bound method object all the time
+        # Cache a bound method on the instance, so that we don't have to
+        # re-create a bound method object all the time.
         self._cached_bound_method_trace = self._trace
 
-
     def __repr__(self):
         return "<PyTracer at 0x{:x}: {} lines in {} files>".format(
             id(self),
@@ -289,7 +288,7 @@ def stop(self):
             dont_warn = (env.PYPY and env.PYPYVERSION >= (5, 4) and self.in_atexit and tf is None)
             if (not dont_warn) and tf != self._cached_bound_method_trace:   # pylint: disable=comparison-with-callable
                 self.warn(
-                    f"Trace function changed, data is likely wrong: "
+                    "Trace function changed, data is likely wrong: " +
                     f"{tf!r} != {self._cached_bound_method_trace!r}",
                     slug="trace-changed",
                 )