diff --git a/Sources/Foundation/FileManager+POSIX.swift b/Sources/Foundation/FileManager+POSIX.swift
index a400abb830..cf7573ba14 100644
--- a/Sources/Foundation/FileManager+POSIX.swift
+++ b/Sources/Foundation/FileManager+POSIX.swift
@@ -584,7 +584,7 @@ extension FileManager {
         }
         defer { close(srcfd) }
 
-        let dstfd = open(dstRep, O_WRONLY | O_CREAT | O_TRUNC, 0o666)
+        let dstfd = open(dstRep, O_WRONLY | O_CREAT | O_EXCL | O_TRUNC, 0o666)
         guard dstfd >= 0 else {
             throw _NSErrorWithErrno(errno, reading: false, path: dstPath,
                                     extraUserInfo: extraErrorInfo(srcPath: srcPath, dstPath: dstPath, userVariant: variant))
diff --git a/Sources/Foundation/FileManager+Win32.swift b/Sources/Foundation/FileManager+Win32.swift
index 8fea257006..6d325c79cc 100644
--- a/Sources/Foundation/FileManager+Win32.swift
+++ b/Sources/Foundation/FileManager+Win32.swift
@@ -476,7 +476,7 @@ extension FileManager {
 
     internal func _copyRegularFile(atPath srcPath: String, toPath dstPath: String, variant: String = "Copy") throws {
       try FileManager.default._fileSystemRepresentation(withPath: srcPath, andPath: dstPath) {
-        if !CopyFileW($0, $1, false) {
+        if !CopyFileW($0, $1, true) {
           throw _NSErrorWithWindowsError(GetLastError(), reading: true, paths: [srcPath, dstPath])
         }
       }