diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
index c3d2a2b..0b93b52 100755
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -28,7 +28,7 @@
 -W/--verbose3   -- display test output on failure
 -d/--debug      -- print traceback for failed tests
 -q/--quiet      -- no output unless one or more tests fail
--S/--slow       -- print the slowest 10 tests
+-o/--slow       -- print the slowest 10 tests
    --header     -- print header with interpreter info
 
 Selecting tests
@@ -312,7 +312,7 @@
             start = a
         elif o in ('-s', '--single'):
             single = True
-        elif o in ('-S', '--slow'):
+        elif o in ('-o', '--slow'):
             print_slow = True
         elif o in ('-r', '--randomize'):
             randomize = True
diff --git a/Misc/NEWS b/Misc/NEWS
index 8e95abb..073417d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -97,6 +97,9 @@
 Library
 -------
 
+- Issue #13726: Fix the ambiguous -S flag in regrtest. It is -o/--slow for slow
+  tests.
+
 - Issue #12364: Fix a hang in concurrent.futures.ProcessPoolExecutor.
   The hang would occur when retrieving the result of a scheduled future after
   the executor had been shut down.