diff --git a/Lib/test/test_cmd_line.py b/Lib/test/test_cmd_line.py
index 72edc2e..ef3c109 100644
--- a/Lib/test/test_cmd_line.py
+++ b/Lib/test/test_cmd_line.py
@@ -171,6 +171,16 @@
         self.assertEqual(rc, 0)
         self.assert_(data.startswith(b'x'), data)
 
+    def test_large_PYTHONPATH(self):
+        with test.support.EnvironmentVarGuard() as env:
+            path1 = "ABCDE" * 100
+            path2 = "FGHIJ" * 100
+            env['PYTHONPATH'] = path1 + os.pathsep + path2
+            p = _spawn_python('-S', '-c', 'import sys; print(sys.path)')
+            stdout, _ = p.communicate()
+            self.assert_(path1.encode('ascii') in stdout)
+            self.assert_(path2.encode('ascii') in stdout)
+
 
 def test_main():
     test.support.run_unittest(CmdLineTest)
diff --git a/Misc/NEWS b/Misc/NEWS
index 1aa84d2..b4e2557 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@
 Core and Builtins
 -----------------
 
+- Issue #5924: On Windows, a large PYTHONPATH environment variable
+  (more than 255 characters) would be completely ignored.
+
 - Issue #4547: When debugging a very large function, it was not always
   possible to update the lineno attribute of the current frame.
 
diff --git a/PC/getpathp.c b/PC/getpathp.c
index 36abbf2..212f942 100644
--- a/PC/getpathp.c
+++ b/PC/getpathp.c
@@ -424,8 +424,6 @@
 	wchar_t *buf;
 	size_t bufsz;
 	wchar_t *pythonhome = Py_GetPythonHome();
-	char *_envpath = Py_GETENV("PYTHONPATH");
-	wchar_t wenvpath[MAXPATHLEN+1];
 	wchar_t *envpath = NULL;
 
 #ifdef MS_WINDOWS
@@ -434,13 +432,20 @@
 	wchar_t *userpath = NULL;
 	wchar_t zip_path[MAXPATHLEN+1];
 	size_t len;
-#endif
+
+	if (!Py_IgnoreEnvironmentFlag) {
+		envpath = _wgetenv(L"PYTHONPATH");
+	}
+#else
+	char *_envpath = Py_GETENV("PYTHONPATH");
+	wchar_t wenvpath[MAXPATHLEN+1];
 	if (_envpath) {
 		size_t r = mbstowcs(wenvpath, _envpath, MAXPATHLEN+1);
 		envpath = wenvpath;
 		if (r == (size_t)-1 || r >= MAXPATHLEN)
 			envpath = NULL;
 	}
+#endif
 
 	get_progpath();
 	/* progpath guaranteed \0 terminated in MAXPATH+1 bytes. */