diff --git a/Lib/test/test_trace.py b/Lib/test/test_trace.py
--- a/Lib/test/test_trace.py
+++ b/Lib/test/test_trace.py
@@ -1,9 +1,10 @@
 import os
+import pickle
 import sys
 from test.support import TESTFN, rmtree, unlink, captured_stdout
 from test.support.script_helper import assert_python_ok, assert_python_failure
 import unittest
 
 import trace
 from trace import Trace
 
@@ -345,16 +346,24 @@ class TestCoverage(unittest.TestCase):
         for line in stdout:
             lines, cov, module = line.split()[:3]
             coverage[module] = (int(lines), int(cov[:-1]))
         # XXX This is needed to run regrtest.py as a script
         modname = trace._fullmodname(sys.modules[modname].__file__)
         self.assertIn(modname, coverage)
         self.assertEqual(coverage[modname], (5, 100))
 
+    def test_coverageresults_update(self):
+        outfile = TESTFN + '-outfile'
+        with open(outfile, 'wb') as f:
+            pickle.dump(({}, {}, {'caller': 1}), f, protocol=1)
+        self.addCleanup(unlink, outfile)
+        results = trace.CoverageResults({}, {}, outfile, {})
+        self.assertEqual(results.callers, {'caller': 1})
+
 ### Tests that don't mess with sys.settrace and can be traced
 ### themselves TODO: Skip tests that do mess with sys.settrace when
 ### regrtest is invoked with -T option.
 class Test_Ignore(unittest.TestCase):
     def test_ignored(self):
         jn = os.path.join
         ignore = trace._Ignore(['x', 'y.z'], [jn('foo', 'bar')])
         self.assertTrue(ignore.names('x.py', 'x'))
diff --git a/Lib/trace.py b/Lib/trace.py
--- a/Lib/trace.py
+++ b/Lib/trace.py
@@ -179,22 +179,22 @@ class CoverageResults:
             self.calledfuncs = {}
         self.calledfuncs = self.calledfuncs.copy()
         self.callers = callers
         if self.callers is None:
             self.callers = {}
         self.callers = self.callers.copy()
         self.infile = infile
         self.outfile = outfile
-        if self.infile:
+        if self.infile is not None:
             # Try to merge existing counts file.
             try:
                 with open(self.infile, 'rb') as f:
                     counts, calledfuncs, callers = pickle.load(f)
-                self.update(self.__class__(counts, calledfuncs, callers))
+                self.update(CoverageResults(counts, calledfuncs, callers=callers))
             except (OSError, EOFError, ValueError) as err:
                 print(("Skipping counts file %r: %s"
                                       % (self.infile, err)), file=sys.stderr)
 
     def is_ignored_filename(self, filename):
         """Return True if the filename does not refer to a file
         we want to have reported.
         """