diff --git a/R/as-tsibble.R b/R/as-tsibble.R
index 0a5178d3..ca8f649c 100644
--- a/R/as-tsibble.R
+++ b/R/as-tsibble.R
@@ -498,7 +498,7 @@ duplicated_key_index <- function(data, key, index) {
   # time zone associated with the index will be dropped,
   # e.g. nycflights13::weather, thus result in duplicates.
   # dup <- anyDuplicated(data[, identifiers, drop = FALSE])
-  res <- grouped_df(data, vars = key) %>%
+  res <- grouped_df(as_tibble(data), key) %>%
     summarise(!! "zzz" := anyDuplicated.default(!! index)) %>%
     dplyr::pull(!! "zzz")
   any_not_equal_to_c(res, 0)
diff --git a/R/index-by.R b/R/index-by.R
index 122f6f32..c04ddc66 100644
--- a/R/index-by.R
+++ b/R/index-by.R
@@ -78,11 +78,10 @@ index_by.tbl_ts <- function(.data, ...) {
   if (identical(idx_chr, expr_name)) {
     abort(sprintf("Column `%s` (index) can't be overwritten.", idx_chr))
   }
+  idx2 <- sym(expr_name)
   # ungroup() protect the index class
   tbl <- mutate(ungroup(.data), !!! exprs) %>% 
-    group_by(!!! groups(.data)) %>% 
-    new_tsibble_class("grouped_ts")
-  idx2 <- sym(expr_name)
+    group_by(!!! groups(.data), !! idx2)
   build_tsibble(
     tbl, key = key(.data), index = !! idx, index2 = !! idx2,
     regular = is_regular(.data), validate = FALSE,
diff --git a/R/key-group.R b/R/key-group.R
index 1b6f941a..ba65faec 100644
--- a/R/key-group.R
+++ b/R/key-group.R
@@ -56,11 +56,12 @@ key_by.tbl_ts <- function(.data, ...) {
   exprs <- enexprs(...)
   key <- validate_key(.data, exprs)
   validate <- !all(is.element(key(.data), key))
+  idx <- index(.data)
   if (validate) {
-    .data <- retain_tsibble(.data, key, index(.data))
+    .data <- retain_tsibble(.data, key, idx)
   }
   build_tsibble_meta(
-    .data, key = key, index = !! index(.data), index2 = !! index2(.data),
+    .data, key = key, index = !! idx, index2 = !! index2(.data),
     regular = is_regular(.data), ordered = is_ordered(.data), 
     interval = interval(.data)
   )
@@ -118,7 +119,7 @@ key_indices <- function(x) {
 #' @export
 key_indices.tbl_ts <- function(x) {
   key_vars <- key_vars(x)
-  grped_key <- grouped_df(x, key_vars)
+  grped_key <- grouped_df(as_tibble(x), key_vars)
   group_indices(grped_key)
 }
 
diff --git a/tests/testthat/test-tsibble.R b/tests/testthat/test-tsibble.R
index 52817cfa..e05c5490 100644
--- a/tests/testthat/test-tsibble.R
+++ b/tests/testthat/test-tsibble.R
@@ -64,7 +64,7 @@ test_that("nanotime with 1 nanoseconds interval", {
 
 test_that("POSIXt with 1 second interval", {
   expect_identical(index_valid(dat_x$date_time), TRUE)
-  expect_message(tsbl <- as_tsibble(dat_x))
+  expect_message(tsbl <- as_tsibble(dat_x), "Using `date_time` as index variable.")
   expect_output(print(tsbl), "A tsibble: 5 x 2 \\[1s\\]")
   expect_error(as_tsibble(dat_x, key = id(date_time)))
   expect_is(tsbl, "tbl_ts")