diff --git a/NEWS.md b/NEWS.md
index a2d8807b..9e88bdfc 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,7 @@
 # haven (development version)
 
+* `labelled()` tests that value labels are unique (@larmarange, #364).
+
 * `as_factor(x)` is now faster when `x` does not contain any missing values
   (@hughparsonage).
 
diff --git a/R/labelled.R b/R/labelled.R
index a15dced5..d4dd2160 100644
--- a/R/labelled.R
+++ b/R/labelled.R
@@ -48,6 +48,9 @@ labelled <- function(x, labels, label = NULL) {
   if (is.null(names(labels))) {
     stop("`labels` must have names", call. = FALSE)
   }
+  if (any(duplicated(stats::na.omit(labels)))) {
+    stop("`labels` must be unique", call. = FALSE)
+  }
   if (!is.null(label) && (!is.character(label) || length(label) != 1)) {
     stop("`label` must be a character vector of length one", call. = FALSE)
   }
diff --git a/tests/testthat/test-labelled.R b/tests/testthat/test-labelled.R
index bcffb7bf..c5d41851 100644
--- a/tests/testthat/test-labelled.R
+++ b/tests/testthat/test-labelled.R
@@ -23,6 +23,10 @@ test_that("label must be length 1 character or missing", {
                "character vector of length one")
 })
 
+test_that("labels must be unique", {
+  expect_error(labelled(1, c(female = 1, male = 1)), "must be unique")
+})
+
 # methods -----------------------------------------------------------------
 
 test_that("printed output is stable", {
diff --git a/tests/testthat/test-labelled_spss.R b/tests/testthat/test-labelled_spss.R
index 185ed8f5..cb4f14ed 100644
--- a/tests/testthat/test-labelled_spss.R
+++ b/tests/testthat/test-labelled_spss.R
@@ -32,6 +32,11 @@ test_that("subsetting preserves attributes", {
   expect_identical(x, x[])
 })
 
+test_that("labels must be unique", {
+  expect_error(
+    labelled_spss(1, c(female = 1, male = 1), na_values = 9),
+    "must be unique")
+})
 
 # is.na -------------------------------------------------------------------