procedural grounds more than 30 days after the filing of the notice of removal exceeded court’s authority); 14A C. Wright, A. Miller & E. Cooper, Federal Practice and Procedure § 3739, at 166 (Supp.1993) (“[T]he 30-day limit applies to all motions to remand except in eases in which the court lacks subject-matter jurisdiction.”).
Section 1447(d) provides that, except in a case removed pursuant to 28 U.S.C. § 1443 (permitting defendant to remove civil rights case), “[a]n order remanding a case to the State court from which it was removed is not reviewable on appeal or otherwise.” 28 U.S.C. § 1447(d). Despite its facial breadth, this provision insulates from appellate review only those remand orders that are authorized by § 1447(c). See Gravitt v. Southwestern Bell Telephone Co., 430 U.S. 723, 723-24 (1977) (per curiam); Thermtron Products, Inc. v. Hermansdorfer, 423 U.S. 336, 346, 96 S.Ct. 584, 591, 46 L.Ed.2d 542 (1976) (“only remand orders issued under § 1447(c) and invoking the grounds specified therein ... are immune from review under § 1447(d)”). Though Gravitt and Thermtron were construing a pre-1988 version of § 1447(e) that required the district court to remand a case if it appeared, prior to final judgment, that the action “was removed improvidently and without jurisdiction,” 28 U.S.C. § 1447(c) (1982), we see no sound basis for believing that the principle established is not equally applicable to the present version of that section. See, e.g., In re Shell Oil Co., 932 F.2d 1518, 1519-21 (5th Cir.1991) (applying Thermtron to the 1988 version of § 1447(c)), cert. denied, — U.S. —, 112 S.Ct. 914, 116 L.Ed.2d 814 (1992); Air-Shields, Inc. v. Fullam, 891 F.2d at 66 (same).
Reading the present §§ 1447(c) and (d) together, we conclude that an order granting remand based either on a timely motion asserting a procedural defect or on a lack of federal subject matter jurisdiction is not reviewable. However, an order remanding on procedural grounds either upon an untimely motion or sua spowte more than 30 days after removal, since such an order is not authorized by § 1447(c), is reviewable.
Finally, we note that because an order remanding a removed action is not a final judgment, the proper vehicle for review is normally mandamus, not appeal. See Thermtron Products, Inc. v. Hermansdorfer, 423 U.S. at 352-53, 96 S.Ct. at 593-94. This Court has discretion, however, to treat a notice of appeal as a petition for mandamus. See, e.g., Corcoran v. Ardra Insurance Co., 842 F.2d 31, 35 (2d Cir.1988).
The Present Lawsuit
Hamilton commenced the present action pro se in Connecticut Superior Court in March 1982. In August 1989, he removed the action to federal court; he was allowed to file an amended removal petition in January 1990. Aetna made no motion for a remand to state court, but moved to dismiss the action for lack of subject matter jurisdiction in June 1992. The district court, in an endorsed order dated July 22, 1992, construed Aetna’s dismissal motion as one for remand and granted the motion.
Had the district court premised its remand on lack of federal subject matter jurisdiction, the remand order would not be reviewable, and we would dismiss this appeal for lack of appellate jurisdiction. However, in ordering the remand, the court stated only that “[pjlaintiff patently lacked the right to remove his own case from state to federal court.” Since the court did not address the merits of Aetna’s jurisdictional challenge, we construe the order as a ruling that the removal was procedurally improper, not that the action was one over which the court had no subject matter jurisdiction.
Although the court was correct in its observation that there was no authority permitting Hamilton to remove his own action to federal court, that defect was waived by the failure of Aetna, or the court sua spowte, to raise the matter within 30 days of removal. Given the passage of more than 30 days without a challenge, the court lacked authority under § 1447(c) to remand the action on that ground. Since the removal order was not authorized by § 1447(c), it is reviewable.
Treating Hamilton’s notice of appeal as a petition for mandamus, we reject his contention that the action should not have been remanded to state court. His complaint did