diff -r 5b253d641826 Lib/test/test_trace.py
--- a/Lib/test/test_trace.py	Wed Nov 09 18:56:26 2016 -0500
+++ b/Lib/test/test_trace.py	Thu Nov 10 12:12:50 2016 +0200
@@ -311,11 +311,11 @@ class TestCoverage(unittest.TestCase):
         with captured_stdout() as stdout:
             self._coverage(tracer)
         stdout = stdout.getvalue()
-        self.assertTrue("pprint.py" in stdout)
-        self.assertTrue("case.py" in stdout)   # from unittest
+        self.assertIn("pprint.py", stdout)
+        self.assertIn("case.py", stdout)   # from unittest
         files = os.listdir(TESTFN)
-        self.assertTrue("pprint.cover" in files)
-        self.assertTrue("unittest.case.cover" in files)
+        self.assertIn("pprint.cover", files)
+        self.assertIn("unittest.case.cover", files)
 
     def test_coverage_ignore(self):
         # Ignore all files, nothing should be traced nor printed
diff -r 5b253d641826 Modules/getpath.c
--- a/Modules/getpath.c	Wed Nov 09 18:56:26 2016 -0500
+++ b/Modules/getpath.c	Thu Nov 10 12:12:50 2016 +0200
@@ -719,9 +719,14 @@ calculate_path(void)
     while (1) {
         wchar_t *delim = wcschr(defpath, DELIM);
 
-        if (defpath[0] != SEP)
+        if (defpath[0] != SEP) {
             /* Paths are relative to prefix */
             bufsz += prefixsz;
+            if (prefixsz >= 2 && prefix[prefixsz - 2] != SEP &&
+                defpath[0] != (delim ? DELIM : L'\0')) {  /* not empty */
+                bufsz++;
+            }
+        }
 
         if (delim)
             bufsz += delim - defpath + 1;
@@ -762,7 +767,10 @@ calculate_path(void)
 
         if (defpath[0] != SEP) {
             wcscat(buf, prefix);
-            wcscat(buf, separator);
+            if (prefixsz >= 2 && prefix[prefixsz - 2] != SEP &&
+                defpath[0] != (delim ? DELIM : L'\0')) {  /* not empty */
+                wcscat(buf, separator);
+            }
         }
 
         if (delim) {