The identity of Azara's No. 240 “Cola aguda cola de canela obscura” and the name Sylvia ruficollisVieillot, 1817 which is based on it has been widely discussed, but never convincingly elucidated. Azara obtained the specimen from the “barbarians of Paraguay” and the distinctive tail pattern that he described narrows the identity down to three species in the Paraguayan avifauna, two in the genus Asthenes and Phacellodomus sibilatrix. Much confusion about the identity of Azara's birds has been previously caused by Vieillot's tendency to omit the morphometrics provided in the original description. In this case, it is possible to confirm the identity of Sylvia ruficollis as Phacellodomus sibilatrix. In order to maintain nomenclatural stability, it is recommended that the older name Sylvia ruficollis be suppressed.