diff --git a/Sources/X509/Verifier/RFC5280/URIConstraints.swift b/Sources/X509/Verifier/RFC5280/URIConstraints.swift
index a2c3f523..ac83fd37 100644
--- a/Sources/X509/Verifier/RFC5280/URIConstraints.swift
+++ b/Sources/X509/Verifier/RFC5280/URIConstraints.swift
@@ -12,8 +12,15 @@
 //
 //===----------------------------------------------------------------------===//
 
-import CoreFoundation
 import Foundation
+#if os(Windows)
+import WinSDK
+#elseif os(Linux) || os(Android)
+import Glibc
+import CoreFoundation
+#elseif os(iOS) || os(macOS) || os(tvOS) || os(watchOS)
+import Darwin
+#endif
 
 extension NameConstraintsPolicy {
     /// Validates that a URI name matches a name constraint.
@@ -58,14 +65,22 @@ extension NameConstraintsPolicy {
 extension String {
     @inlinable
     var isIPAddress: Bool {
+#if os(Windows)
+        var v4: IN_ADDR = IN_ADDR()
+        var v6: IN6_ADDR = IN6_ADDR()
+        return self.withCString(encodedAs: UTF16.self) {
+            return InetPtonW(AF_INET, $0, &v4) == 1 ||
+                   InetPtonW(AF_INET6, $0, &v6) == 1
+        }
+#else
         // We need some scratch space to let inet_pton write into.
         var ipv4Addr = in_addr()
         var ipv6Addr = in6_addr()
-
         return self.withCString { ptr in
             return inet_pton(AF_INET, ptr, &ipv4Addr) == 1 ||
                    inet_pton(AF_INET6, ptr, &ipv6Addr) == 1
         }
+#endif
     }
 }