diff --git a/src/fns.c b/src/fns.c
index c3202495da..f5e2584587 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -2668,7 +2668,8 @@ DEFUN ("mapconcat", Fmapconcat, Smapconcat, 3, 3, 0,
        doc: /* Apply FUNCTION to each element of SEQUENCE, and concat the results as strings.
 In between each pair of results, stick in SEPARATOR.  Thus, " " as
 SEPARATOR results in spaces between the values returned by FUNCTION.
-SEQUENCE may be a list, a vector, a bool-vector, or a string.  */)
+SEQUENCE may be a list, a vector, etc. see `mapcar'.
+SEPARATOR and all values returned by FUNCTION must be accepted by `concat'.  */)
   (Lisp_Object function, Lisp_Object sequence, Lisp_Object separator)
 {
   USE_SAFE_ALLOCA;