diff --git a/library/std/src/process.rs b/library/std/src/process.rs
index d88ab625371..9824cce6c72 100644
--- a/library/std/src/process.rs
+++ b/library/std/src/process.rs
@@ -2030,6 +2030,11 @@ pub fn id() -> u32 {
 ///
 /// The default implementations are returning `libc::EXIT_SUCCESS` to indicate
 /// a successful execution. In case of a failure, `libc::EXIT_FAILURE` is returned.
+///
+/// Because different runtimes have different specifications on the return value
+/// of the `main` function, this trait is likely to be available only on
+/// standard library's runtime for convenience. Other runtimes are not required
+/// to provide similar functionality.
 #[cfg_attr(not(test), lang = "termination")]
 #[unstable(feature = "termination_trait_lib", issue = "43301")]
 #[rustc_on_unimplemented(