diff --git a/R/utils.R b/R/utils.R
index 343a69a..1aafa17 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -9,7 +9,7 @@ add_tbl_class <-
 
 
 first_found_in <-
-  function(.x, domain, default = NA) {
+  function(.x, domain, default = NA_character_) {
     .out <- domain[domain %in% .x][1L]
     if (is.na(.out)) { .out <- default }
     .out
@@ -18,9 +18,9 @@ first_found_in <-
 
 index_of_first_found_in <-
   function(.x, domain, default = NA_integer_) {
-    .out <- which(.x %in% domain)[1L]
-    if (is.na(.out)) { .out <- default }
-    .out
+    .out <- first_found_in(.x, domain)
+    if (is.na(.out)) { return(default) }
+    which(.x == .out)
   }
 
 
diff --git a/tests/testthat/test-utils.R b/tests/testthat/test-utils.R
index aca25f1..012fe63 100644
--- a/tests/testthat/test-utils.R
+++ b/tests/testthat/test-utils.R
@@ -25,3 +25,37 @@ test_that("format_force_data_link_data_frame() works as expected", {
   expect_type(result[[1L]], "character")
   expect_type(result[[2L]], "character")
 })
+
+test_that("first_found_in() works as expected", {
+  # same order
+  .x <- c("A", "B", "C")
+  domain <- c("A", "C")
+  expect_equal(first_found_in(.x, domain), "A")
+
+  # out of order
+  .x <- c("A", "B", "C")
+  domain <- c("B", "A")
+  expect_equal(first_found_in(.x, domain), "B")
+
+  # `NA` if none found
+  .x <- c("a", "b")
+  domain <- c("source", "from", "sources", "start", "begin")
+  expect_equal(first_found_in(.x, domain), NA_character_)
+})
+
+test_that("index_of_first_found_in() works as expected", {
+  # same order
+  .x <- c("A", "B", "C")
+  domain <- c("A", "C")
+  expect_equal(index_of_first_found_in(.x, domain), 1L)
+
+  # out of order
+  .x <- c("A", "B", "C")
+  domain <- c("B", "A")
+  expect_equal(index_of_first_found_in(.x, domain), 2L)
+
+  # `NA` if none found
+  .x <- c("a", "b")
+  domain <- c("source", "from", "sources", "start", "begin")
+  expect_equal(index_of_first_found_in(.x, domain), NA_integer_)
+})