diff --git a/plugins/relay.py b/plugins/relay.py
index eab73be..f2e09c0 100644
--- a/plugins/relay.py
+++ b/plugins/relay.py
@@ -176,17 +176,19 @@ def normalize_host(irc, host):
     """Creates a normalized hostname for the given host suitable for
     introduction to a remote network (as a relay client)."""
     log.debug('(%s) relay.normalize_host: IRCd=%s, host=%s', irc.name, irc.protoname, host)
-    if irc.protoname not in ('inspircd', 'ts6', 'clientbot', 'nefarious'):
+
+    allowed_chars = string.ascii_letters + string.digits + '-.:'
+    if irc.protoname in ('inspircd', 'ts6', 'clientbot', 'nefarious'):
         # UnrealIRCd and IRCd-Hybrid don't allow slashes in hostnames
-        host = host.replace('/', '.')
-    host = host.replace('\x03', '')  # Strip colours
-    host = host.replace('\x02', '')  # Strip bold
-    host = host.replace('\x1f', '')  # Strip underline
-    host = host.replace('\x1d', '')  # Strip italic
-    host = host.replace('\x0f', '')  # Strip color reset
-    host = host.replace('\x16', '')  # Strip reverse color
-    # And no, I'm not supporting colours in hosts. Screw your IRCd-breaking patches if you think
-    # this is cool. -GL
+        allowed_chars += '/'
+
+    if irc.protoname in ('inspircd', 'clientbot', 'nefarious', 'unreal'):
+        # The above IRCds allow _ in hostnames, while TS6-like IRCds do not.
+        allowed_chars += '_'
+
+    for char in host:
+        if char not in allowed_chars:
+            host = host.replace(char, '-')
 
     return host[:63]  # Limit hosts to 63 chars for best compatibility
 
diff --git a/protocols/hybrid.py b/protocols/hybrid.py
index 05c282a..a79bf93 100644
--- a/protocols/hybrid.py
+++ b/protocols/hybrid.py
@@ -168,6 +168,7 @@ class HybridProtocol(TS6Protocol):
         """
         # <- :0UY UID dan 1 1451041551 +Facdeiklosuw ~ident localhost 127.0.0.1 0UYAAAAAB * :realname
         nick = args[0]
+        self.checkCollision(nick)
         ts, modes, ident, host, ip, uid, account, realname = args[2:10]
         if account == '*':
             account = None
diff --git a/protocols/inspircd.py b/protocols/inspircd.py
index e1568b0..8dbf7de 100644
--- a/protocols/inspircd.py
+++ b/protocols/inspircd.py
@@ -561,6 +561,7 @@ class InspIRCdProtocol(TS6BaseProtocol):
         """Handles incoming UID commands (user introduction)."""
         # :70M UID 70MAAAAAB 1429934638 GL 0::1 hidden-7j810p.9mdf.lrek.0000.0000.IP gl 0::1 1429934638 +Wioswx +ACGKNOQXacfgklnoqvx :realname
         uid, ts, nick, realhost, host, ident, ip = args[0:7]
+        self.checkCollision(nick)
         realname = args[-1]
         self.irc.users[uid] = userobj = IrcUser(nick, ts, uid, numeric, ident, host, realname, realhost, ip)
 
diff --git a/protocols/ircs2s_common.py b/protocols/ircs2s_common.py
index c0e92ba..c8542fb 100644
--- a/protocols/ircs2s_common.py
+++ b/protocols/ircs2s_common.py
@@ -7,6 +7,18 @@ from pylinkirc.log import log
 
 class IRCS2SProtocol(Protocol):
 
+    def checkCollision(self, nick):
+        """
+        Nick collision checker.
+        """
+        uid = self.irc.nickToUid(nick)
+        # If there is a nick collision, we simply alert plugins. Relay will purposely try to
+        # lose fights and tag nicks instead, while other plugins can choose how to handle this.
+        if uid:
+            log.info('(%s) Nick collision on %s/%s, forwarding this to plugins', self.irc.name,
+                     uid, nick)
+            self.irc.callHooks([self.irc.sid, 'SAVE', {'target': uid}])
+
     def handle_kill(self, source, command, args):
         """Handles incoming KILLs."""
         killed = args[0]
diff --git a/protocols/nefarious.py b/protocols/nefarious.py
index 0daba13..8f1ae62 100644
--- a/protocols/nefarious.py
+++ b/protocols/nefarious.py
@@ -827,6 +827,7 @@ class P10Protocol(IRCS2SProtocol):
             # <- AB N GL 1 1460673049 ~gl nefarious.midnight.vpn +iw B]AAAB ABAAA :realname
 
             nick = args[0]
+            self.checkCollision(nick)
             ts, ident, host = args[2:5]
             realhost = host
             ip = args[-3]
diff --git a/protocols/ts6.py b/protocols/ts6.py
index 82c1681..505df58 100644
--- a/protocols/ts6.py
+++ b/protocols/ts6.py
@@ -499,6 +499,7 @@ class TS6Protocol(TS6BaseProtocol):
         """Handles incoming EUID commands (user introduction)."""
         # <- :42X EUID GL 1 1437505322 +ailoswz ~gl 127.0.0.1 127.0.0.1 42XAAAAAB * * :realname
         nick = args[0]
+        self.checkCollision(nick)
         ts, modes, ident, host, ip, uid, realhost, accountname, realname = args[2:11]
         if realhost == '*':
             realhost = None
diff --git a/protocols/unreal.py b/protocols/unreal.py
index 7abaf0a..d3a4934 100644
--- a/protocols/unreal.py
+++ b/protocols/unreal.py
@@ -336,6 +336,7 @@ class UnrealProtocol(TS6BaseProtocol):
         # arguments: nick, hopcount?, ts, ident, real-host, UID, services account (0 if none), modes,
         #            displayed host, cloaked (+x) host, base64-encoded IP, and realname
         nick = args[0]
+        self.checkCollision(nick)
         ts, ident, realhost, uid, accountname, modestring, host = args[2:9]
 
         if host == '*':