Clarence Nash, an inmate at the Federal Medical Center (FMC), appeals the district court’s 1 preservice dismissal of his 42 U.S.C. § 1983 complaint for failure to exhaust administrative remedies.

While the exhaustion requirement is an affirmative defense that a defendant must plead and prove, see Nerness v. Johnson, 401 F.3d 874, 876 (8th Cir. 2005) (per curiam), it is clear from the dates of the alleged incidents that Nash could not have administratively exhausted all of his claims when he filed the instant lawsuit, cf. Myers v. Vogal, 960 F.2d 750, 751 (8th Cir. 1992) (per curiam) (while statute of limitations is affirmative defense, district court may properly dismiss in forma pauperis complaint before service when it is apparent from face of complaint that statute of limitations has run). Accordingly, we affirm but modify the dismissal to be without prejudice. See Calico Trailer Mfg. Co. v. Ins. Co. of N. Am., 155 F.3d 976, 978 (8th Cir. 1998) (modifying dismissal for failure to exhaust administrative remedies to be dismissal without prejudice).