diff --git a/R/means_by_group.R b/R/means_by_group.R
index 4b66e776d..e61de1a6f 100644
--- a/R/means_by_group.R
+++ b/R/means_by_group.R
@@ -7,7 +7,8 @@
 #' @param group If `x` is a numeric vector, `group` should be a factor that
 #' indicates the group-classifying categories. If `x` is a data frame, `group`
 #' should be a character string, naming the variable in `x` that is used for
-#' grouping. Numeric vectors are coerced to factors.
+#' grouping. Numeric vectors are coerced to factors. Not that `group` should
+#' only refer to a single variable.
 #' @param ci Level of confidence interval for mean estimates. Default is `0.95`.
 #' Use `ci = NA` to suppress confidence intervals.
 #' @param weights If `x` is a numeric vector, `weights` should be a vector of
diff --git a/man/means_by_group.Rd b/man/means_by_group.Rd
index 3c9d7c7d8..f02cebcf8 100644
--- a/man/means_by_group.Rd
+++ b/man/means_by_group.Rd
@@ -32,7 +32,8 @@ means_by_group(x, ...)
 \item{group}{If \code{x} is a numeric vector, \code{group} should be a factor that
 indicates the group-classifying categories. If \code{x} is a data frame, \code{group}
 should be a character string, naming the variable in \code{x} that is used for
-grouping. Numeric vectors are coerced to factors.}
+grouping. Numeric vectors are coerced to factors. Not that \code{group} should
+only refer to a single variable.}
 
 \item{ci}{Level of confidence interval for mean estimates. Default is \code{0.95}.
 Use \code{ci = NA} to suppress confidence intervals.}