diff --git a/Lib/test/test_thread.py b/Lib/test/test_thread.py

index 413889a..fb312aa 100644

--- a/Lib/test/test_thread.py

+++ b/Lib/test/test_thread.py

@@ -237,7 +237,12 @@ class TestForkInThread(unittest.TestCase):

             if pid == 0: # child

                 os.close(self.read_fd)

                 os.write(self.write_fd, "OK")

-                sys.exit(0)

+                # Exiting the thread normally in the child process can leave

+                # any additional threads (such as the one started by

+                # importing _tkinter) still running, and this can prevent

+                # the half-zombie child process from being cleaned up. See

+                # Issue #26456.

+                os._exit(0)

             else: # parent

                 os.close(self.write_fd)