diff --git a/R/as-tsibble.R b/R/as-tsibble.R
index 8f3ebe34..018bfe46 100644
--- a/R/as-tsibble.R
+++ b/R/as-tsibble.R
@@ -299,7 +299,7 @@ as.tibble.tbl_ts <- as_tibble.tbl_ts
 as_tibble.grouped_ts <- function(x, ...) {
   grps <- groups(x)
   class(x) <- c("grouped_df", "tbl_df", "tbl", "data.frame")
-  attr(x, "vars") <- grps
+  attr(x, "vars") <- flatten(grps)
   x
 }
 
diff --git a/R/parse-key.R b/R/parse-key.R
index d8ced71d..fae3695a 100644
--- a/R/parse-key.R
+++ b/R/parse-key.R
@@ -11,6 +11,7 @@ reduce_key <- function(lst_keys) {
   quos_auto_name(comb_keys)
 }
 
+# this returns a vector of groups/key characters
 flatten_key <- function(lst_keys) {
   if (is.null(lst_keys)) {
     lst_keys <- list()