diff --git a/R/utility.R b/R/utility.R
index d85cff9..e09d70c 100644
--- a/R/utility.R
+++ b/R/utility.R
@@ -26,7 +26,7 @@ as_cordf <- function(x, diagonal = NA) {
     stop("Input object x is not a square. ",
          "The number of columns must be equal to the number of rows.")
   }
-  diag(x) <- diagonal
+  if (ncol(x) > 1) diag(x) <- diagonal
   new_cordf(x, names(x))
 }
 
diff --git a/tests/testthat/test-correlate.R b/tests/testthat/test-correlate.R
index ea970f1..5062d56 100644
--- a/tests/testthat/test-correlate.R
+++ b/tests/testthat/test-correlate.R
@@ -18,3 +18,16 @@ test_that("Diagonal sets correctly", {
   expect_equal(all(is.na(diag(as.matrix(correlate(d, diagonal = NA)[, -1])))), TRUE)
   expect_equal(all(diag(as.matrix(correlate(d, diagonal = 100)[, -1] == 100))), TRUE)
 })
+
+
+test_that("correlate works with numeric vectors", {
+  expect_equal(correlate(x = 1:10, y = 1:10)[[2]], 1)
+  expect_equal(correlate(x = 1:10, y = -(1:10), diagonal = 0)[[2]], -1)
+})
+
+test_that("correlate works with a one-column data.frame", {
+  var <- "Sepal.Length"
+  expect_equal(correlate(datasets::iris[var])[[1]], var)
+  expect_equal(correlate(datasets::iris[var])[[2]], 1)
+
+})