diff --git a/test/intl/testcfg.py b/test/intl/testcfg.py
index 9fc087e5f5..51fa1e1a88 100644
--- a/test/intl/testcfg.py
+++ b/test/intl/testcfg.py
@@ -46,7 +46,9 @@ class IntlTestSuite(testsuite.TestSuite):
       for filename in files:
         if (filename.endswith(".js") and filename != "assert.js" and
             filename != "utils.js"):
-          testname = os.path.join(dirname[len(self.root) + 1:], filename[:-3])
+          fullpath = os.path.join(dirname, filename)
+          relpath = fullpath[len(self.root) + 1 : -3]
+          testname = relpath.replace(os.path.sep, "/")
           test = testcase.TestCase(self, testname)
           tests.append(test)
     return tests
diff --git a/test/message/testcfg.py b/test/message/testcfg.py
index cfe22f15d7..bc73510c09 100644
--- a/test/message/testcfg.py
+++ b/test/message/testcfg.py
@@ -52,7 +52,9 @@ class MessageTestSuite(testsuite.TestSuite):
       files.sort()
       for filename in files:
         if filename.endswith(".js"):
-          testname = os.path.join(dirname[len(self.root) + 1:], filename[:-3])
+          fullpath = os.path.join(dirname, filename)
+          relpath = fullpath[len(self.root) + 1 : -3]
+          testname = relpath.replace(os.path.sep, "/")
           test = testcase.TestCase(self, testname)
           tests.append(test)
     return tests
diff --git a/test/mjsunit/testcfg.py b/test/mjsunit/testcfg.py
index 4fbdcfca26..7af7acf0a9 100644
--- a/test/mjsunit/testcfg.py
+++ b/test/mjsunit/testcfg.py
@@ -52,7 +52,9 @@ class MjsunitTestSuite(testsuite.TestSuite):
       files.sort()
       for filename in files:
         if filename.endswith(".js") and filename != "mjsunit.js":
-          testname = os.path.join(dirname[len(self.root) + 1:], filename[:-3])
+          fullpath = os.path.join(dirname, filename)
+          relpath = fullpath[len(self.root) + 1 : -3]
+          testname = relpath.replace(os.path.sep, "/")
           test = testcase.TestCase(self, testname)
           tests.append(test)
     return tests
diff --git a/test/mozilla/testcfg.py b/test/mozilla/testcfg.py
index 70a7ac663c..70665cb807 100644
--- a/test/mozilla/testcfg.py
+++ b/test/mozilla/testcfg.py
@@ -81,8 +81,9 @@ class MozillaTestSuite(testsuite.TestSuite):
         files.sort()
         for filename in files:
           if filename.endswith(".js") and not filename in FRAMEWORK:
-            testname = os.path.join(dirname[len(self.testroot) + 1:],
-                                    filename[:-3])
+            fullpath = os.path.join(dirname, filename)
+            relpath = fullpath[len(self.testroot) + 1 : -3]
+            testname = relpath.replace(os.path.sep, "/")
             case = testcase.TestCase(self, testname)
             tests.append(case)
     return tests
diff --git a/test/test262-es6/testcfg.py b/test/test262-es6/testcfg.py
index f9e9a3946b..49a9b254a0 100644
--- a/test/test262-es6/testcfg.py
+++ b/test/test262-es6/testcfg.py
@@ -119,8 +119,9 @@ class Test262TestSuite(testsuite.TestSuite):
       files.sort()
       for filename in files:
         if filename.endswith(".js"):
-          testname = os.path.join(dirname[len(self.testroot) + 1:],
-                                  filename[:-3])
+          fullpath = os.path.join(dirname, filename)
+          relpath = fullpath[len(self.testroot) + 1 : -3]
+          testname = relpath.replace(os.path.sep, "/")
           case = testcase.TestCase(self, testname)
           tests.append(case)
     return tests
diff --git a/test/test262/testcfg.py b/test/test262/testcfg.py
index a0c2cd6568..835c1ffd0b 100644
--- a/test/test262/testcfg.py
+++ b/test/test262/testcfg.py
@@ -66,8 +66,9 @@ class Test262TestSuite(testsuite.TestSuite):
       files.sort()
       for filename in files:
         if filename.endswith(".js"):
-          testname = os.path.join(dirname[len(self.testroot) + 1:],
-                                  filename[:-3])
+          fullpath = os.path.join(dirname, filename)
+          relpath = fullpath[len(self.testroot) + 1 : -3]
+          testname = relpath.replace(os.path.sep, "/")
           case = testcase.TestCase(self, testname)
           tests.append(case)
     return tests
diff --git a/test/webkit/testcfg.py b/test/webkit/testcfg.py
index aa81964f5e..ed811d2922 100644
--- a/test/webkit/testcfg.py
+++ b/test/webkit/testcfg.py
@@ -55,7 +55,9 @@ class WebkitTestSuite(testsuite.TestSuite):
       files.sort()
       for filename in files:
         if filename.endswith(".js"):
-          testname = os.path.join(dirname[len(self.root) + 1:], filename[:-3])
+          fullpath = os.path.join(dirname, filename)
+          relpath = fullpath[len(self.root) + 1 : -3]
+          testname = relpath.replace(os.path.sep, "/")
           test = testcase.TestCase(self, testname)
           tests.append(test)
     return tests
diff --git a/tools/testrunner/local/testsuite.py b/tools/testrunner/local/testsuite.py
index c8e43521e7..e0fff0d11a 100644
--- a/tools/testrunner/local/testsuite.py
+++ b/tools/testrunner/local/testsuite.py
@@ -226,7 +226,7 @@ class TestSuite(object):
         continue
       if len(argpath) == 1 or (len(argpath) == 2 and argpath[1] == '*'):
         return  # Don't filter, run all tests in this suite.
-      path = os.path.sep.join(argpath[1:])
+      path = '/'.join(argpath[1:])
       if path[-1] == '*':
         path = path[:-1]
         globs.append(path)