diff --git a/doc/lispref/internals.texi b/doc/lispref/internals.texi
index 26292d75369..0cb3e0ccb1d 100644
--- a/doc/lispref/internals.texi
+++ b/doc/lispref/internals.texi
@@ -1814,9 +1814,10 @@ returns unique mutable string objects.
 @end deftypefn
 
 @deftypefn Function emacs_value make_unibyte_string (emacs_env *@var{env}, const char *@var{str}, ptrdiff_t @var{len})
-This function is like @code{make_string}, but has no restrictions on
-the values of the bytes in the C string, and can be used to pass
-binary data to Emacs in the form of a unibyte string.
+This function, which is available since Emacs 28, is like
+@code{make_string}, but has no restrictions on the values of the bytes
+in the C string, and can be used to pass binary data to Emacs in the
+form of a unibyte string.
 @end deftypefn
 
 The @acronym{API} does not provide functions to manipulate Lisp data