diff --git a/R/trans.r b/R/trans.r
index 93849a3b..a4f0b662 100644
--- a/R/trans.r
+++ b/R/trans.r
@@ -18,7 +18,8 @@
 #' @param format default format for this transformation. The format is applied
 #'   to breaks generated to the raw data.
 #' @param domain domain, as numeric vector of length 2, over which
-#'   transformation is valued
+#'   transformation is valued. The function in the `transform` argument is
+#'   expected to be able to transform the `domain` argument.
 #' @seealso \Sexpr[results=rd,stage=build]{scales:::seealso_trans()}
 #' @export
 #' @keywords internal
diff --git a/man/trans_new.Rd b/man/trans_new.Rd
index 00d59b0c..eb42efd4 100644
--- a/man/trans_new.Rd
+++ b/man/trans_new.Rd
@@ -39,7 +39,8 @@ function is applied to the raw data.}
 to breaks generated to the raw data.}
 
 \item{domain}{domain, as numeric vector of length 2, over which
-transformation is valued}
+transformation is valued. The function in the \code{transform} argument is
+expected to be able to transform the \code{domain} argument.}
 }
 \description{
 A transformation encapsulates a transformation and its inverse, as well