diff --git a/configargparse.py b/configargparse.py
index 9c2df50..7136c00 100644
--- a/configargparse.py
+++ b/configargparse.py
@@ -784,15 +784,24 @@ def convert_item_to_command_line_arg(self, action, key, value):
             command_line_key = \
                 self.get_command_line_key_for_unknown_config_file_setting(key)
         else:
-            command_line_key = action.option_strings[-1]
+            if not isinstance(action, argparse.BooleanOptionalAction):
+                command_line_key = action.option_strings[-1]
 
         # handle boolean value
         if action is not None and isinstance(action, ACTION_TYPES_THAT_DONT_NEED_A_VALUE):
             if value.lower() in ("true", "yes", "1"):
-                args.append( command_line_key )
+                if not isinstance(action, argparse.BooleanOptionalAction):
+                    args.append( command_line_key )
+                else:
+                    # --foo
+                    args.append(action.option_strings[0])
             elif value.lower() in ("false", "no", "0"):
                 # don't append when set to "false" / "no"
-                pass
+                if not isinstance(action, argparse.BooleanOptionalAction):
+                    pass
+                else:
+                    # --no-foo
+                    args.append(action.option_strings[1])
             elif isinstance(action, argparse._CountAction):
                 for arg in args:
                     if any([arg.startswith(s) for s in action.option_strings]):
diff --git a/tests/test_configargparse.py b/tests/test_configargparse.py
index 2ff5fb9..162b6e7 100644
--- a/tests/test_configargparse.py
+++ b/tests/test_configargparse.py
@@ -97,6 +97,7 @@ def testBasicCase1(self):
         self.add_arg("-x", "--arg-x", action="store_true")
         self.add_arg("-y", "--arg-y", dest="y1", type=int, required=True)
         self.add_arg("--arg-z", action="append", type=float, required=True)
+        self.add_arg('--foo', action=argparse.BooleanOptionalAction, default=False)
 
         # make sure required args are enforced
         self.assertParseArgsRaises("too few arg"
@@ -112,12 +113,13 @@ def testBasicCase1(self):
             args="file1.txt file2.txt file3.txt -x -y 1")
 
         # check values after setting args on command line
-        ns = self.parse(args="file1.txt --arg-x -y 3 --arg-z 10",
+        ns = self.parse(args="file1.txt --arg-x -y 3 --arg-z 10 --foo",
                         config_file_contents="")
         self.assertListEqual(ns.filenames, ["file1.txt"])
         self.assertEqual(ns.arg_x, True)
         self.assertEqual(ns.y1, 3)
         self.assertEqual(ns.arg_z, [10])
+        self.assertEqual(ns.foo, True)
 
         self.assertRegex(self.format_values(),
             'Command Line Args:   file1.txt --arg-x -y 3 --arg-z 10')
@@ -129,23 +131,27 @@ def testBasicCase1(self):
             arg-y = 10
             arg-z = 30
             arg-z = 40
+            foo = True
             """)
         self.assertListEqual(ns.filenames, ["file1.txt", "file2.txt"])
         self.assertEqual(ns.arg_x, True)
         self.assertEqual(ns.y1, 10)
         self.assertEqual(ns.arg_z, [40])
+        self.assertEqual(ns.foo, True)
 
         self.assertRegex(self.format_values(),
             'Command Line Args: \\s+ file1.txt file2.txt\n'
             'Config File \\(method arg\\):\n'
             '  arg-x: \\s+ True\n'
             '  arg-y: \\s+ 10\n'
-            '  arg-z: \\s+ 40\n')
+            '  arg-z: \\s+ 40\n'
+            '  foo: \\s+ True\n')
 
         # check values after setting args in both command line and config file
         ns = self.parse(args="file1.txt file2.txt --arg-x -y 3 --arg-z 100 ",
             config_file_contents="""arg-y = 31.5
                                     arg-z = 30
+                                    foo = True
                                  """)
         self.format_help()
         self.format_values()
@@ -153,6 +159,7 @@ def testBasicCase1(self):
         self.assertEqual(ns.arg_x, True)
         self.assertEqual(ns.y1, 3)
         self.assertEqual(ns.arg_z, [100])
+        self.assertEqual(ns.foo, True)
 
         self.assertRegex(self.format_values(),
             "Command Line Args:   file1.txt file2.txt --arg-x -y 3 --arg-z 100")