diff --git a/R/formatters_var_labels.R b/R/formatters_var_labels.R
index 55cb1fcb9..02e0d2cc6 100644
--- a/R/formatters_var_labels.R
+++ b/R/formatters_var_labels.R
@@ -43,19 +43,24 @@ col_labels <- function(x, fill = FALSE) {
     return(character(0L))
   }
 
-  labels <- lapply(x, function(x) as.vector(attr(x, "label")[[1]]))
-
-  nulls <- vapply(labels, is.null, logical(1L))
-  if (any(nulls)) {
-    labels[nulls] <-
-      if (fill) {
-        colnames(x)[nulls]
+  vapply(
+    colnames(x),
+    function(colname) {
+      label <- as.vector(attr(x[[colname]], "label"))
+      checkmate::assert_string(label, .var.name = sprintf("'%s' column label", colname), null.ok = TRUE)
+      if (is.null(label)) {
+        if (fill) {
+          colname
+        } else {
+          NA_character_
+        }
       } else {
-        NA_character_
+        label
       }
-  }
-
-  unlist(labels)
+    },
+    character(1L),
+    USE.NAMES = TRUE
+  )
 }
 
 #' @rdname col_labels
diff --git a/tests/testthat/test-formatters_var_labels.R b/tests/testthat/test-formatters_var_labels.R
index e00be84f0..d63636eb0 100644
--- a/tests/testthat/test-formatters_var_labels.R
+++ b/tests/testthat/test-formatters_var_labels.R
@@ -25,7 +25,7 @@ testthat::test_that("col_labels works with labels having additional attributes (
   x <- iris
   attr(x$Species, "label") <- structure("Label for Species", names = "blah", foo = "bar")
   testthat::expect_identical(col_labels(x)[["Species"]], "Label for Species")
-)}
+})
 
 testthat::test_that("col_labels returns only 'names' attribute and ignores all the rest", {
   x <- iris
@@ -33,6 +33,24 @@ testthat::test_that("col_labels returns only 'names' attribute and ignores all t
   testthat::expect_identical(attributes(col_labels(x)["Species"]), list(names = "Species"))
 })
 
+testthat::test_that("col_labels throws if label is not a character", {
+  x <- iris
+  attr(x$Species, "label") <- structure(1, names = "blah", foo = "bar")
+  testthat::expect_error(
+    col_labels(x),
+    "Assertion on ''Species' column label' failed"
+  )
+})
+
+testthat::test_that("col_labels throws if label is not a character of length 1", {
+  x <- iris
+  attr(x$Species, "label") <- structure(c("a", "b"), names = "blah", foo = "bar")
+  testthat::expect_error(
+    col_labels(x),
+    "Assertion on ''Species' column label' failed"
+  )
+})
+
 # col_labels ----
 testthat::test_that("col_labels<- value accepts character vector", {
   iris_df <- utils::head(iris, 2)