diff --git a/default.yaml b/default.yaml
index 7936a766..922f3717 100644
--- a/default.yaml
+++ b/default.yaml
@@ -820,6 +820,9 @@ limits:
     # identlen is the max ident length allowed
     identlen: 20
 
+    # realnamelen is the maximum realname length allowed
+    realnamelen: 150
+
     # channellen is the max channel length allowed
     channellen: 64
 
diff --git a/irc/config.go b/irc/config.go
index 3649efd1..8b1312fa 100644
--- a/irc/config.go
+++ b/irc/config.go
@@ -484,6 +484,7 @@ type Limits struct {
 	ChanListModes        int `yaml:"chan-list-modes"`
 	ChannelLen           int `yaml:"channellen"`
 	IdentLen             int `yaml:"identlen"`
+	RealnameLen          int `yaml:"realnamelen"`
 	KickLen              int `yaml:"kicklen"`
 	MonitorEntries       int `yaml:"monitor-entries"`
 	NickLen              int `yaml:"nicklen"`
diff --git a/irc/handlers.go b/irc/handlers.go
index 520f26c1..cfe98572 100644
--- a/irc/handlers.go
+++ b/irc/handlers.go
@@ -3334,6 +3334,10 @@ func userHandler(server *Server, client *Client, msg ircmsg.Message, rb *Respons
 		rb.Add(nil, server.name, ERR_NEEDMOREPARAMS, client.Nick(), "USER", client.t("Not enough parameters"))
 		return false
 	}
+	config := server.Config()
+	if config.Limits.RealnameLen > 0 && len(realname) > config.Limits.RealnameLen {
+		realname = ircmsg.TruncateUTF8Safe(realname, config.Limits.RealnameLen)
+	}
 
 	// #843: we accept either: `USER user:pass@clientid` or `USER user@clientid`
 	if strudelIndex := strings.IndexByte(username, '@'); strudelIndex != -1 {
diff --git a/traditional.yaml b/traditional.yaml
index 22d2b550..84f7b861 100644
--- a/traditional.yaml
+++ b/traditional.yaml
@@ -792,6 +792,9 @@ limits:
     # identlen is the max ident length allowed
     identlen: 20
 
+    # realnamelen is the maximum realname length allowed
+    realnamelen: 150
+
     # channellen is the max channel length allowed
     channellen: 64