diff --git a/src/group_cmd.cpp b/src/group_cmd.cpp
--- a/src/group_cmd.cpp
+++ b/src/group_cmd.cpp
@@ -181,7 +181,7 @@ CommandCost CmdRenameGroup(TileIndex til
 	bool reset = StrEmpty(text);
 
 	if (!reset) {
-		if (strlen(text) >= MAX_LENGTH_GROUP_NAME_BYTES) return CMD_ERROR;
+		if (Utf8StringLength(text) >= MAX_LENGTH_GROUP_NAME_CHARS) return CMD_ERROR;
 		if (!IsUniqueGroupName(text)) return_cmd_error(STR_ERROR_NAME_MUST_BE_UNIQUE);
 	}