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	Wed Jul 11 13:15:05 2012 -0700
@@ -166,6 +166,7 @@
 """
 
 import builtins
+import collections
 import faulthandler
 import getopt
 import io
@@ -611,17 +612,7 @@
         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 = collections.deque(tests)  # thread-safe pops.
         opt_args = support.args_from_interpreter_flags()
         base_cmd = [sys.executable] + opt_args + ['-m', 'test.regrtest']
         def work():
@@ -629,10 +620,17 @@
             try:
                 while True:
                     try:
-                        test, args_tuple = next(pending)
-                    except StopIteration:
+                        test = pending.popleft()
+                    except IndexError:
                         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 +689,7 @@
                 test_index += 1
         except KeyboardInterrupt:
             interrupted = True
-            pending.close()
+            pending.clear()
         for worker in workers:
             worker.join()
     else:
diff -r 4752fafb579d Misc/NEWS
--- a/Misc/NEWS	Wed Jul 11 19:21:31 2012 +0200
+++ b/Misc/NEWS	Wed Jul 11 13:15:05 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.