diff --git a/Sources/ZIPFoundation/Archive+ZIP64.swift b/Sources/ZIPFoundation/Archive+ZIP64.swift
index 2925fbf9..2b519a1c 100644
--- a/Sources/ZIPFoundation/Archive+ZIP64.swift
+++ b/Sources/ZIPFoundation/Archive+ZIP64.swift
@@ -143,8 +143,13 @@ extension Archive.ZIP64EndOfCentralDirectory {
 }
 
 /// Properties that represent the maximum value of each field
+#if swift(>=6.0)
 nonisolated(unsafe) var maxUInt32 = UInt32.max
 nonisolated(unsafe) var maxUInt16 = UInt16.max
+#else
+var maxUInt32 = UInt32.max
+var maxUInt16 = UInt16.max
+#endif
 
 var maxCompressedSize: UInt32 { maxUInt32 }
 var maxUncompressedSize: UInt32 { maxUInt32 }