diff --git a/R/utils.R b/R/utils.R
index 7d237e4e3..abf930c19 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -133,7 +133,12 @@
 #' @keywords internal
 #' @importFrom stats setNames
 .rename_columns <- function(df, new_names, old_names) {
-  are_char <- is.character(new_names) & is.character(old_names)
+  if (is.null(new_names) | is.null(old_names)) {
+    return(df)
+  }
+  new_char <- sapply(new_names, is.character)
+  old_char <- sapply(old_names, is.character)
+  are_char <- new_char & old_char
   valid_new_names <- new_names[are_char]
   valid_old_names <- old_names[are_char]
   if (length(are_char) > 0) {
diff --git a/tests/testthat/test-utils.R b/tests/testthat/test-utils.R
index 5b9701aaf..e8d0fc7cd 100644
--- a/tests/testthat/test-utils.R
+++ b/tests/testthat/test-utils.R
@@ -70,3 +70,16 @@ test_that(".make_intercepts_explicit does not add an intercept if the distributi
   attr(formula_updated$pforms$sigma, ".Environment") <- NULL
   expect_equal(formula, formula_updated)
 })
+
+test_that(".rename_columns works correctly", { # nolint: line_length_linter.
+  df <- data.frame(a = 1, b = 2)
+  new_df <- .rename_columns(df, new_names = c("x", "y"), old_names = c("a", "b"))
+  expect_named(new_df, c("x", "y"))
+})
+
+test_that(".rename_columns does nothing if old_names is only NULL", { # nolint: line_length_linter.
+  df <- data.frame(a = 1, b = 2)
+  new_df <- .rename_columns(df, new_names = c("a", "b"), old_names = c(NULL, NULL))
+  expect_named(new_df, c("a", "b"))
+})
+