diff --git a/src/os/exec/exec.go b/src/os/exec/exec.go
index 41fbf963708..88b0a916992 100644
--- a/src/os/exec/exec.go
+++ b/src/os/exec/exec.go
@@ -113,6 +113,8 @@ type Cmd struct {
 	// ExtraFiles specifies additional open files to be inherited by the
 	// new process. It does not include standard input, standard output, or
 	// standard error. If non-nil, entry i becomes file descriptor 3+i.
+	//
+	// ExtraFiles is not supported on Windows.
 	ExtraFiles []*os.File
 
 	// SysProcAttr holds optional, operating system-specific attributes.