diff --git a/ircstates/__init__.py b/ircstates/__init__.py
index b206b08..6a13823 100644
--- a/ircstates/__init__.py
+++ b/ircstates/__init__.py
@@ -2,5 +2,5 @@ from .server       import Server, ServerDisconnectedException
 from .user         import User
 from .channel      import Channel
 from .channel_user import ChannelUser
-from .casemap      import casefold
+from .casemap      import casefold, CaseMap
 from .emit         import *
diff --git a/ircstates/casemap.py b/ircstates/casemap.py
index 0782453..8cdba1e 100644
--- a/ircstates/casemap.py
+++ b/ircstates/casemap.py
@@ -1,24 +1,24 @@
-import string
-from typing import List
-from cachetools import cached, LRUCache
+from enum import Enum
+from string import ascii_lowercase, ascii_uppercase
+from typing import Dict, List
 
-ASCII_UPPER   = list(string.ascii_uppercase)
-ASCII_LOWER   = list(string.ascii_lowercase)
-RFC1459_UPPER = ASCII_UPPER+list("[]^\\")
-RFC1459_LOWER = ASCII_LOWER+list("{}~|")
+class CaseMap(Enum):
+    ASCII = "ascii"
+    RFC1459 = "rfc1459"
 
-def _replace(s: str, upper: List[str], lower: List[str]):
-    out = ""
-    for char in s:
-        if char in upper:
-            out += lower[upper.index(char)]
-        else:
-            out += char
-    return out
+def _make_trans(upper: str, lower: str):
+    return str.maketrans(dict(zip(upper, lower)))
 
-@cached(cache=LRUCache(maxsize=1024))
-def casefold(mapping: str, s: str):
-    if mapping   == "rfc1459":
-        return _replace(s, RFC1459_UPPER, RFC1459_LOWER)
-    elif mapping == "ascii":
-        return _replace(s, ASCII_UPPER,   ASCII_LOWER)
+CASEMAPS: Dict[CaseMap, Dict[int, str]] = {
+    CaseMap.ASCII: _make_trans(
+        r"ABCDEFGHIJKLMNOPQRSTUVWXYZ",
+        r"abcdefghijklmnopqrstuvwxyz"
+    ),
+    CaseMap.RFC1459: _make_trans(
+        r"ABCDEFGHIJKLMNOPQRSTUVWXYZ\[]^",
+        r"abcdefghijklmnopqrstuvwxyz|{}~"
+    )
+}
+def casefold(casemap_name: CaseMap, s: str):
+    casemap = CASEMAPS[casemap_name]
+    return s.translate(casemap)
diff --git a/ircstates/isupport/__init__.py b/ircstates/isupport/__init__.py
index e0c3260..17e9383 100644
--- a/ircstates/isupport/__init__.py
+++ b/ircstates/isupport/__init__.py
@@ -1,5 +1,6 @@
 from typing import Dict, List, Optional
 from .tokens import ChanModes, Prefix
+from ..casemap import CaseMap
 
 CASEMAPPINGS = ["rfc1459", "ascii"]
 
@@ -31,7 +32,7 @@ class ISupport(object):
     prefix    = Prefix(["o", "v"], ["@", "+"])
 
     modes:       int       = 3 # -1 if "no limit"
-    casemapping: str       = "rfc1459"
+    casemapping: CaseMap   = CaseMap.RFC1459
     chantypes:   List[str] = ["#"]
     statusmsg:   List[str] = []
 
@@ -75,8 +76,7 @@ class ISupport(object):
                 self.watch   = int(value) if value else -1
 
             elif key == "CASEMAPPING":
-                if value in CASEMAPPINGS:
-                    self.casemapping = value
+                self.casemapping = CaseMap(value)
 
             elif key == "CHANTYPES":
                 self.chantypes = list(value)
diff --git a/test/casemap.py b/test/casemap.py
index 740988f..9da28ac 100644
--- a/test/casemap.py
+++ b/test/casemap.py
@@ -3,11 +3,11 @@ import ircstates, irctokens
 
 class CaseMapTestMethod(unittest.TestCase):
     def test_rfc1459(self):
-        lower = ircstates.casefold("rfc1459", "ÀTEST[]^\\")
+        lower = ircstates.casefold(ircstates.CaseMap.RFC1459, "ÀTEST[]^\\")
         self.assertEqual(lower, "Àtest{}~|")
 
     def test_ascii(self):
-        lower = ircstates.casefold("ascii", "ÀTEST[]~\\")
+        lower = ircstates.casefold(ircstates.CaseMap.ASCII, "ÀTEST[]~\\")
         self.assertEqual(lower, "Àtest[]~\\")
 
 class CaseMapTestCommands(unittest.TestCase):
diff --git a/test/isupport.py b/test/isupport.py
index 8b68170..b57c29c 100644
--- a/test/isupport.py
+++ b/test/isupport.py
@@ -58,25 +58,6 @@ class ISUPPORTTest(unittest.TestCase):
         server.parse_tokens(irctokens.tokenise("005 * MODES=5 *"))
         self.assertEqual(server.isupport.modes, 5)
 
-    def test_rfc1459(self):
-        server = ircstates.Server("test")
-        server.parse_tokens(irctokens.tokenise("001 nickname *"))
-        self.assertEqual(server.isupport.casemapping, "rfc1459")
-        server.parse_tokens(irctokens.tokenise("005 * CASEMAPPING=rfc1459 *"))
-        self.assertEqual(server.isupport.casemapping, "rfc1459")
-
-    def test_ascii(self):
-        server = ircstates.Server("test")
-        server.parse_tokens(irctokens.tokenise("001 nickname *"))
-        server.parse_tokens(irctokens.tokenise("005 * CASEMAPPING=ascii *"))
-        self.assertEqual(server.isupport.casemapping, "ascii")
-
-    def test_fallback_to_rfc1459(self):
-        server = ircstates.Server("test")
-        server.parse_tokens(irctokens.tokenise("001 nickname *"))
-        server.parse_tokens(irctokens.tokenise("005 * CASEMAPPING=asd *"))
-        self.assertEqual(server.isupport.casemapping, "rfc1459")
-
     def test_network(self):
         server = ircstates.Server("test")
         server.parse_tokens(irctokens.tokenise("001 nickname *"))
@@ -149,3 +130,23 @@ class ISUPPORTTest(unittest.TestCase):
         self.assertEqual(server.isupport.nicklen, 9)
         server.parse_tokens(irctokens.tokenise("005 * NICKLEN=16 *"))
         self.assertEqual(server.isupport.nicklen, 16)
+
+class ISupportTestCasemapping(unittest.TestCase):
+    def test_rfc1459(self):
+        server = ircstates.Server("test")
+        server.parse_tokens(irctokens.tokenise("001 nickname *"))
+        self.assertEqual(server.isupport.casemapping, ircstates.CaseMap.RFC1459)
+        server.parse_tokens(irctokens.tokenise("005 * CASEMAPPING=rfc1459 *"))
+        self.assertEqual(server.isupport.casemapping, ircstates.CaseMap.RFC1459)
+
+    def test_ascii(self):
+        server = ircstates.Server("test")
+        server.parse_tokens(irctokens.tokenise("001 nickname *"))
+        server.parse_tokens(irctokens.tokenise("005 * CASEMAPPING=ascii *"))
+        self.assertEqual(server.isupport.casemapping, ircstates.CaseMap.ASCII)
+
+    def test_unknown(self):
+        server = ircstates.Server("test")
+        server.parse_tokens(irctokens.tokenise("001 nickname *"))
+        with self.assertRaises(ValueError):
+            server.parse_tokens(irctokens.tokenise("005 * CASEMAPPING=asd *"))