This court granted Christopher Emerson, Texas prisoner # 451863, a certificate of appealability (“COA”) to appeal the dismissal of his 28 U.S.C. § 2254 petition as an unauthorized successive petition. See Emerson v. Thaler, No. 10-20732, slip op. (5th Cir. May 16, 2011). Emerson, however, has not briefed the issue on which COA was granted, i.e., whether, under Castro v. United States, 540 U.S. 375, 383-84, 124 S.Ct. 786, 157 L.Ed.2d 778 (2003), his prior pleading should count for purposes of the successive-authorization requirement. See id.

Contrary to Emerson’s assertion in his reply brief, this court did not hold that Castro is applicable to his case. See Emerson, No. 10-20732, slip op. at 2. We stated that it is arguable that Castro is applicable. See id. Emerson makes no argument that Castro is applicable, that he was not warned of the consequences of the recharacterization of his 2007 pleading as a § 2254 petition, or that, because Castro is applicable and he was not warned, the recharacterization does not count as a pri- or petition for successive-authorization purposes. Although pro se briefs are liberally construed, even pro se litigants must brief arguments to preserve them. Yohey v. Collins, 985 F.2d 222, 224-25 (5th Cir. 1993). Because Emerson has failed to brief the sole issue on which a COA was granted, he has waived that issue, and the *347 judgment is AFFIRMED. Emerson’s motion to supplement the record is DENIED.