diff -r 4752fafb579d Lib/test/regrtest.py
--- a/Lib/test/regrtest.py	Wed Jul 11 19:21:31 2012 +0200
+++ b/Lib/test/regrtest.py	Sun Jul 15 15:41:26 2012 -0700
@@ -611,17 +611,7 @@
         from subprocess import Popen, PIPE
         debug_output_pat = re.compile(r"\[\d+ refs\]$")
         output = Queue()
-        def tests_and_args():
-            for test in tests:
-                args_tuple = (
-                    (test, verbose, quiet),
-                    dict(huntrleaks=huntrleaks, use_resources=use_resources,
-                         debug=debug, output_on_failure=verbose3,
-                         timeout=timeout, failfast=failfast,
-                         match_tests=match_tests)
-                )
-                yield (test, args_tuple)
-        pending = tests_and_args()
+        pending = MultiprocessTests(tests)
         opt_args = support.args_from_interpreter_flags()
         base_cmd = [sys.executable] + opt_args + ['-m', 'test.regrtest']
         def work():
@@ -629,10 +619,17 @@
             try:
                 while True:
                     try:
-                        test, args_tuple = next(pending)
+                        test = next(pending)
                     except StopIteration:
                         output.put((None, None, None, None))
                         return
+                    args_tuple = (
+                        (test, verbose, quiet),
+                        dict(huntrleaks=huntrleaks, use_resources=use_resources,
+                             debug=debug, output_on_failure=verbose3,
+                             timeout=timeout, failfast=failfast,
+                             match_tests=match_tests)
+                    )
                     # -E is needed by some tests, e.g. test_import
                     # Running the child from the same working directory ensures
                     # that TEMPDIR for the child is the same when
@@ -691,7 +688,7 @@
                 test_index += 1
         except KeyboardInterrupt:
             interrupted = True
-            pending.close()
+            pending.interrupted = True
         for worker in workers:
             worker.join()
     else:
@@ -837,6 +834,25 @@
             tests.append(mod)
     return stdtests + sorted(tests)
 
+# We do not use a generator so multiple threads can call next().
+class MultiprocessTests(object):
+
+    """A thread-safe iterator over tests for multiprocess mode."""
+
+    def __init__(self, tests):
+        self.interrupted = False
+        self.lock = threading.Lock()
+        self.tests = tests
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        with self.lock:
+            if self.interrupted:
+                raise StopIteration('tests interrupted')
+            return next(self.tests)
+
 def replace_stdout():
     """Set stdout encoder error handler to backslashreplace (as stderr error
     handler) to avoid UnicodeEncodeError when printing a traceback"""
diff -r 4752fafb579d Misc/NEWS
--- a/Misc/NEWS	Wed Jul 11 19:21:31 2012 +0200
+++ b/Misc/NEWS	Sun Jul 15 15:41:26 2012 -0700
@@ -121,6 +121,9 @@
 Tests
 -----
 
+- Issue #15320: Make iterating the list of tests thread-safe when running
+  tests in multiprocess mode. Patch by Chris Jerdonek.
+
 - Issue #15300: Ensure the temporary test working directories are in the same
   parent folder when running tests in multiprocess mode from a Python build.
   Patch by Chris Jerdonek.