diff --git a/Sources/System/FileOperations.swift b/Sources/System/FileOperations.swift
index a8b107cd..055daeea 100644
--- a/Sources/System/FileOperations.swift
+++ b/Sources/System/FileOperations.swift
@@ -401,7 +401,6 @@ extension FileDescriptor {
 }
 #endif
 
-#if !os(Windows)
 /*System 1.2.0, @available(macOS 9999, iOS 9999, watchOS 9999, tvOS 9999, *)*/
 extension FileDescriptor {
   /// Truncate or extend the file referenced by this file descriptor.
@@ -447,4 +446,3 @@ extension FileDescriptor {
     }
   }
 }
-#endif
diff --git a/Sources/System/Internals/WindowsSyscallAdapters.swift b/Sources/System/Internals/WindowsSyscallAdapters.swift
index 36acaceb..13f42c96 100644
--- a/Sources/System/Internals/WindowsSyscallAdapters.swift
+++ b/Sources/System/Internals/WindowsSyscallAdapters.swift
@@ -105,4 +105,11 @@ internal func pwrite(
   return Int(nNumberOfBytesWritten)
 }
 
+@inline(__always)
+internal func ftruncate(
+  _ fd: Int32,
+  _ length: off_t
+) -> Int32 {
+  _chsize_s(fd, numericCast(length))
+}
 #endif