diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index eb7d1a4..23ec399 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -799,6 +799,7 @@
         old = sys.getfilesystemencoding()
         sys.setfilesystemencoding("iso-8859-1")
         self.assertEqual(sys.getfilesystemencoding(), "iso-8859-1")
+        self.assertRaises(LookupError, sys.setfilesystemencoding, "xxx")
         sys.setfilesystemencoding(old)
 
 def test_main():
diff --git a/Misc/NEWS b/Misc/NEWS
index 0d316a0..8a63a22 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@
 Core and Builtins
 -----------------
 
+- Issue #8226: sys.setfilesystemencoding() raises a LookupError if the encoding
+  is unknown
+
 - Issue #1583863: An str subclass can now override the __str__ method
 
 - Issue #8014: Setting a T_UINT or T_PYSSIZET attribute of an object with
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index a928fc4..6b8600b 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -29,7 +29,7 @@
 int
 _Py_SetFileSystemEncoding(PyObject *s)
 {
-	PyObject *defenc;
+	PyObject *defenc, *codec;
 	if (!PyUnicode_Check(s)) {
 		PyErr_BadInternalCall();
 		return -1;
@@ -37,6 +37,10 @@
 	defenc = _PyUnicode_AsDefaultEncodedString(s, NULL);
 	if (!defenc)
 		return -1;
+	codec = _PyCodec_Lookup(PyBytes_AsString(defenc));
+	if (codec == NULL)
+		return -1;
+	Py_DECREF(codec);
 	if (!Py_HasFileSystemDefaultEncoding && Py_FileSystemDefaultEncoding)
 		/* A file system encoding was set at run-time */
 		free((char*)Py_FileSystemDefaultEncoding);