diff --git a/Lib/fontTools/ufoLib/filenames.py b/Lib/fontTools/ufoLib/filenames.py
index ec33b452a..baf22076c 100644
--- a/Lib/fontTools/ufoLib/filenames.py
+++ b/Lib/fontTools/ufoLib/filenames.py
@@ -3,11 +3,88 @@ User name to file name conversion.
 This was taken from the UFO 3 spec.
 """
 
-illegalCharacters = r"\" * + / : < > ? [ \ ] | \0".split(" ")
-illegalCharacters += [chr(i) for i in range(1, 32)]
-illegalCharacters += [chr(0x7F)]
-reservedFileNames = "CON PRN AUX CLOCK$ NUL A:-Z: COM1".lower().split(" ")
-reservedFileNames += "LPT1 LPT2 LPT3 COM2 COM3 COM4".lower().split(" ")
+# Restrictions are taken mostly from
+# https://docs.microsoft.com/en-gb/windows/win32/fileio/naming-a-file#naming-conventions.
+#
+# 1. Integer value zero, sometimes referred to as the ASCII NUL character.
+# 2. Characters whose integer representations are in the range 1 to 31,
+#    inclusive.
+# 3. Various characters that (mostly) Windows and POSIX-y filesystems don't
+#    allow, plus "(" and ")", as per the specification.
+illegalCharacters = {
+    "\x00",
+    "\x01",
+    "\x02",
+    "\x03",
+    "\x04",
+    "\x05",
+    "\x06",
+    "\x07",
+    "\x08",
+    "\t",
+    "\n",
+    "\x0b",
+    "\x0c",
+    "\r",
+    "\x0e",
+    "\x0f",
+    "\x10",
+    "\x11",
+    "\x12",
+    "\x13",
+    "\x14",
+    "\x15",
+    "\x16",
+    "\x17",
+    "\x18",
+    "\x19",
+    "\x1a",
+    "\x1b",
+    "\x1c",
+    "\x1d",
+    "\x1e",
+    "\x1f",
+    '"',
+    "*",
+    "+",
+    "/",
+    ":",
+    "<",
+    ">",
+    "?",
+    "[",
+    "\\",
+    "]",
+    "(",
+    ")",
+    "|",
+    "\x7f",
+}
+reservedFileNames = {
+    "aux",
+    "clock$",
+    "com1",
+    "com2",
+    "com3",
+    "com4",
+    "com5",
+    "com6",
+    "com7",
+    "com8",
+    "com9",
+    "con",
+    "lpt1",
+    "lpt2",
+    "lpt3",
+    "lpt4",
+    "lpt5",
+    "lpt6",
+    "lpt7",
+    "lpt8",
+    "lpt9",
+    "nul",
+    "prn",
+}
 maxFileNameLength = 255
 
 
diff --git a/Tests/ufoLib/filenames_test.py b/Tests/ufoLib/filenames_test.py
index a9415a1c2..bad413530 100644
--- a/Tests/ufoLib/filenames_test.py
+++ b/Tests/ufoLib/filenames_test.py
@@ -29,6 +29,16 @@ class TestFilenames(unittest.TestCase):
         self.assertEqual(userNameToFileName("con.alt"), "_con.alt")
         self.assertEqual(userNameToFileName("alt.con"), "alt._con")
 
+        self.assertEqual(
+            # Test output for ASCII range (up until 0x7F), except for illegal
+            # characters.
+            userNameToFileName("".join([chr(i) for i in range(0, 0x80)])),
+            "________________________________"
+            " !_#$%&'____,-._0123456789_;_=__"
+            "@A_B_C_D_E_F_G_H_I_J_K_L_M_N_O_P_Q_R_S_T_U_V_W_X_Y_Z_"
+            "___^_`abcdefghijklmnopqrstuvwxyz{_}~_",
+        )
+
     def test_userNameToFileName_ValueError(self):
         with self.assertRaises(ValueError):
             userNameToFileName(b"a")