--- Lib/test/test_warnings.py
+++ Lib/test/test_warnings.py
@@ -758,9 +758,25 @@
                 "-c", "import sys; sys.stdout.write(str(sys.warnoptions))"],
                 stdout=subprocess.PIPE, env=newenv)
         self.assertEqual(p.communicate()[0],
-                b"['ignore::UnicodeWarning', 'ignore::DeprecationWarning']")
+                b"['ignore::DeprecationWarning', 'ignore::UnicodeWarning']")
         self.assertEqual(p.wait(), 0)
 
+    def test_conflicting_envvar_and_command_line(self):
+        newenv = os.environ.copy()
+        newenv["PYTHONWARNINGS"] = "default::DeprecationWarning"
+        p = subprocess.Popen([sys.executable, "-W" "error::DeprecationWarning",
+                "-c", "import sys, warnings; sys.stdout.write(str(sys.warnoptions));"
+                "warnings.warn('Message', DeprecationWarning)"],
+                stdout=subprocess.PIPE, stderr=subprocess.PIPE, env=newenv)
+        stdout, stderr = p.communicate()
+        self.assertEqual(stdout,
+                b"['default::DeprecationWarning', 'error::DeprecationWarning']")
+        self.assertEqual(stderr,
+                b"Traceback (most recent call last):\n"
+                b"  File \"<string>\", line 1, in <module>\n"
+                b"DeprecationWarning: Message\n")
+        self.assertEqual(p.wait(), 1)
+
     @unittest.skipUnless(sys.getfilesystemencoding() != 'ascii',
                          'requires non-ascii filesystemencoding')
     def test_nonascii(self):
--- Modules/main.c
+++ Modules/main.c
@@ -343,6 +343,8 @@
     int version = 0;
     int saw_unbuffered_flag = 0;
     PyCompilerFlags cf;
+    PyObject *warning_option = NULL;
+    PyObject *warning_options = NULL;
 
     cf.cf_flags = 0;
 
@@ -465,7 +467,15 @@
             break;
 
         case 'W':
-            PySys_AddWarnOption(_PyOS_optarg);
+            if (warning_options == NULL)
+                warning_options = PyList_New(0);
+            if (warning_options == NULL)
+                Py_FatalError("failure in handling of -W argument");
+            warning_option = PyUnicode_FromWideChar(_PyOS_optarg, -1);
+            if (warning_option == NULL)
+                Py_FatalError("failure in handling of -W argument");
+            PyList_Append(warning_options, warning_option);
+            Py_DECREF(warning_option);
             break;
 
         case 'X':
@@ -559,6 +569,12 @@
         PyMem_RawFree(buf);
     }
 #endif
+    if (warning_options != NULL) {
+        Py_ssize_t i;
+        for (i = 0; i < PyList_GET_SIZE(warning_options); i++) {
+            PySys_AddWarnOptionUnicode(PyList_GET_ITEM(warning_options, i));
+        }
+    }
 
     if (command == NULL && module == NULL && _PyOS_optind < argc &&
         wcscmp(argv[_PyOS_optind], L"-") != 0)