diff --git a/Sources/X509/CertificatePrivateKey.swift b/Sources/X509/CertificatePrivateKey.swift
index 0d8b8172..f1082ed1 100644
--- a/Sources/X509/CertificatePrivateKey.swift
+++ b/Sources/X509/CertificatePrivateKey.swift
@@ -15,7 +15,7 @@
 import SwiftASN1
 import Foundation
 @preconcurrency import Crypto
-@preconcurrency import _CryptoExtras
+import _CryptoExtras
 
 extension Certificate {
     /// A private key that can be used with a certificate.
diff --git a/Sources/X509/CertificatePublicKey.swift b/Sources/X509/CertificatePublicKey.swift
index c709c035..9d9c4dd6 100644
--- a/Sources/X509/CertificatePublicKey.swift
+++ b/Sources/X509/CertificatePublicKey.swift
@@ -14,7 +14,7 @@
 
 import SwiftASN1
 @preconcurrency import Crypto
-@preconcurrency import _CryptoExtras
+import _CryptoExtras
 import Foundation
 
 extension Certificate {
diff --git a/Sources/X509/Error.swift b/Sources/X509/Error.swift
index a53615b5..984abac0 100644
--- a/Sources/X509/Error.swift
+++ b/Sources/X509/Error.swift
@@ -249,6 +249,9 @@ public struct CertificateError: Error, Hashable, CustomStringConvertible {
     }
 }
 
+// `CertificateError` is `Sendable` because it uses CoW
+extension CertificateError: @unchecked Sendable {}
+
 extension CertificateError {
     /// Represents the kind of an error.
     ///
diff --git a/Sources/X509/OCSP/OCSPPolicy.swift b/Sources/X509/OCSP/OCSPPolicy.swift
index 78863bf0..9b32f6fd 100644
--- a/Sources/X509/OCSP/OCSPPolicy.swift
+++ b/Sources/X509/OCSP/OCSPPolicy.swift
@@ -320,6 +320,7 @@ extension OCSPVerifierPolicy.Storage {
             return responderURI
         }.first
         guard let responderURI else {
+            let ocspAccessDescriptions = Array(ocspAccessDescriptions)
             return self.softFailure(
                 reason: .init("expected OCSP location to be a URI but got \(ocspAccessDescriptions)")
             )
diff --git a/Sources/X509/PromiseAndFuture.swift b/Sources/X509/PromiseAndFuture.swift
index b1e3a8c9..fab152e4 100644
--- a/Sources/X509/PromiseAndFuture.swift
+++ b/Sources/X509/PromiseAndFuture.swift
@@ -13,7 +13,7 @@
 //===----------------------------------------------------------------------===//
 
 // MARK: - Promise
-final class Promise<Value, Failure: Error> {
+final class Promise<Value: Sendable, Failure: Error> {
     private enum State {
         case unfulfilled(observers: [CheckedContinuation<Result<Value, Failure>, Never>])
         case fulfilled(Result<Value, Failure>)
@@ -83,7 +83,7 @@ extension Promise {
 
 // MARK: - Future
 
-struct Future<Value, Failure: Error> {
+struct Future<Value: Sendable, Failure: Error> {
     private let promise: Promise<Value, Failure>
 
     init(_ promise: Promise<Value, Failure>) {
diff --git a/Sources/X509/Signature.swift b/Sources/X509/Signature.swift
index 400fc10f..fe31f8fb 100644
--- a/Sources/X509/Signature.swift
+++ b/Sources/X509/Signature.swift
@@ -13,7 +13,7 @@
 //===----------------------------------------------------------------------===//
 
 import SwiftASN1
-@preconcurrency import _CryptoExtras
+import _CryptoExtras
 import Foundation
 
 extension Certificate {