diff --git a/R/list-transpose.R b/R/list-transpose.R
index 136d60c3..8112f65a 100644
--- a/R/list-transpose.R
+++ b/R/list-transpose.R
@@ -14,9 +14,9 @@
 #' @param x A list of vectors to transpose.
 #' @param template A "template" that describes the output list. Can either be
 #'   a character vector (where elements are extracted by name), or an integer
-#'   vector (where elements are extracted by position). Defaults to the names
-#'   of the first element of `x`, or if they're not present, the integer
-#'   indices.
+#'   vector (where elements are extracted by position). Defaults to the union
+#'   of the names of the elements of `x`, or if they're not present, the
+#'   union of the integer indices.
 #' @param simplify Should the result be [simplified][list_simplify]?
 #'   * `TRUE`: simplify or die trying.
 #'   * `NA`: simplify if possible.
@@ -75,7 +75,7 @@ list_transpose <- function(x,
   if (length(x) == 0) {
     template <- integer()
   } else {
-    template <- template %||% vec_index(x[[1]])
+    template <- template %||% reduce(map(x, vec_index), vec_set_union)
   }
 
   if (!is.character(template) && !is.numeric(template)) {
diff --git a/man/list_transpose.Rd b/man/list_transpose.Rd
index 0dc8aabc..1e86d708 100644
--- a/man/list_transpose.Rd
+++ b/man/list_transpose.Rd
@@ -20,9 +20,9 @@ list_transpose(
 
 \item{template}{A "template" that describes the output list. Can either be
 a character vector (where elements are extracted by name), or an integer
-vector (where elements are extracted by position). Defaults to the names
-of the first element of \code{x}, or if they're not present, the integer
-indices.}
+vector (where elements are extracted by position). Defaults to the union
+of the names of the elements of \code{x}, or if they're not present, the
+union of the integer indices.}
 
 \item{simplify}{Should the result be \link[=list_simplify]{simplified}?
 \itemize{
diff --git a/tests/testthat/test-list-transpose.R b/tests/testthat/test-list-transpose.R
index 272c8a49..398e233a 100644
--- a/tests/testthat/test-list-transpose.R
+++ b/tests/testthat/test-list-transpose.R
@@ -13,7 +13,7 @@ test_that("can use character template", {
   # Default:
   expect_equal(
     list_transpose(x, default = NA),
-    list(a = c(1, NA), b = c(2, 3))
+    list(a = c(1, NA), b = c(2, 3), c = c(NA, 4))
   )
 
   # Change order
@@ -130,3 +130,10 @@ test_that("validates inputs", {
     list_transpose(list(1), template = mean)
   })
 })
+
+test_that("fail mixing named and unnamed vectors", {
+  x <- list(list(a = 1, b = 2), list(a = 3, b = 4))
+  expect_snapshot(error = TRUE, {
+    list_transpose(list(x = list(a = 1, b = 2), y = list(3, 4)))
+  })
+})