diff --git a/Sources/Testing/Support/FileHandle.swift b/Sources/Testing/Support/FileHandle.swift
index 453cedcd0..9aca4a671 100644
--- a/Sources/Testing/Support/FileHandle.swift
+++ b/Sources/Testing/Support/FileHandle.swift
@@ -52,6 +52,21 @@ struct FileHandle: ~Copyable, Sendable {
   /// - Throws: Any error preventing the stream from being opened.
   init(atPath path: String, mode: String) throws {
 #if os(Windows)
+    // Special-case CONOUT$ to map to stdout. This way, if somebody specifies
+    // CONOUT$ as the target path for XML or JSON output from `swift test`,
+    // output will be correctly interleaved with writes to `stdout`. If we don't
+    // do this, the file will open successfully but will be opened in text mode
+    // (even if we ask for binary mode), will wrap at the virtual console's
+    // column limit, and won't share a file lock with the C `stdout` handle.
+    //
+    // To our knowledge, this sort of special-casing is not required on
+    // POSIX-like platforms (i.e. when opening "/dev/stdout"), but it can be
+    // adapted for use there if some POSIX-like platform does need it.
+    if path == "CONOUT$" && mode.contains("w") {
+      self = .stdout
+      return
+    }
+
     // Windows deprecates fopen() as insecure, so call _wfopen_s() instead.
     let fileHandle = try path.withCString(encodedAs: UTF16.self) { path in
       try mode.withCString(encodedAs: UTF16.self) { mode in