diff --git a/Lib/argparse.py b/Lib/argparse.py
index 9c710cef5b6aaa..032d958bb4daf2 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1162,6 +1162,13 @@ def add_parser(self, name, **kwargs):
 
         aliases = kwargs.pop('aliases', ())
 
+        if name in self._name_parser_map:
+            raise ArgumentError(self, _('conflicting subparser: %s') % name)
+        for alias in aliases:
+            if alias in self._name_parser_map:
+                raise ArgumentError(
+                    self, _('conflicting subparser alias: %s') % alias)
+
         # create a pseudo-action to hold the choice help
         if 'help' in kwargs:
             help = kwargs.pop('help')
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index 9899a53d6d1974..9ce3cc913423d1 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -4603,6 +4603,19 @@ def test_resolve_error(self):
               --spam NEW_SPAM
             '''))
 
+    def test_subparser_conflict(self):
+        parser = argparse.ArgumentParser()
+        sp = parser.add_subparsers()
+        sp.add_parser('fullname', aliases=['alias'])
+        self.assertRaises(argparse.ArgumentError,
+                          sp.add_parser, 'fullname')
+        self.assertRaises(argparse.ArgumentError,
+                          sp.add_parser, 'alias')
+        self.assertRaises(argparse.ArgumentError,
+                          sp.add_parser, 'other', aliases=['fullname'])
+        self.assertRaises(argparse.ArgumentError,
+                          sp.add_parser, 'other', aliases=['alias'])
+
 
 # =============================
 # Help and Version option tests
diff --git a/Misc/NEWS.d/next/Library/2020-02-22-12-02-11.bpo-39716.z2WhDQ.rst b/Misc/NEWS.d/next/Library/2020-02-22-12-02-11.bpo-39716.z2WhDQ.rst
new file mode 100644
index 00000000000000..f122811e6bfe3b
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-02-22-12-02-11.bpo-39716.z2WhDQ.rst
@@ -0,0 +1,3 @@
+Raise an ArgumentError when the same subparser name is added twice to an
+`argparse.ArgumentParser`.  This is consistent with the (default) behavior
+when the same option string is added twice to an ArgumentParser.