diff --git a/R/utils.R b/R/utils.R
index 410ad9d1ef..918f8534d8 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -25,14 +25,21 @@ get_client_timezone <- function(ns) {
 #' @keywords internal
 get_teal_bs_theme <- function() {
   bs_theme <- getOption("teal.bs_theme")
+
   if (is.null(bs_theme)) {
-    NULL
-  } else if (!inherits(bs_theme, "bs_theme")) {
-    warning("teal.bs_theme has to be of a bslib::bs_theme class, the default shiny bootstrap is used.")
-    NULL
-  } else {
-    bs_theme
+    return(NULL)
+  }
+
+  if (!checkmate::test_class(bs_theme, "bs_theme")) {
+    warning(
+      "Assertion on 'teal.bs_theme' option value failed: ",
+      checkmate::check_class(bs_theme, "bs_theme"),
+      ". The default Shiny Bootstrap theme will be used."
+    )
+    return(NULL)
   }
+
+  bs_theme
 }
 
 #' Return parentnames along with datanames.
diff --git a/tests/testthat/test-utils.R b/tests/testthat/test-utils.R
index 628f389162..dc171b5bf3 100644
--- a/tests/testthat/test-utils.R
+++ b/tests/testthat/test-utils.R
@@ -4,10 +4,10 @@ testthat::test_that("get_teal_bs_theme", {
     testthat::expect_s3_class(get_teal_bs_theme(), "bs_theme")
   })
   withr::with_options(list("teal.bs_theme" = 1), {
-    testthat::expect_warning(get_teal_bs_theme(), "the default shiny bootstrap is used")
+    testthat::expect_warning(get_teal_bs_theme(), ".*The default Shiny Bootstrap theme will be used.")
   })
   withr::with_options(list("teal.bs_theme" = "bs_theme"), {
-    testthat::expect_warning(get_teal_bs_theme(), "the default shiny bootstrap is used")
+    testthat::expect_warning(get_teal_bs_theme(), ".*The default Shiny Bootstrap theme will be used.")
   })
 })