diff --git a/R/prep_trajectory.R b/R/prep_trajectory.R
index bdf30e56..c26a2ed4 100644
--- a/R/prep_trajectory.R
+++ b/R/prep_trajectory.R
@@ -33,7 +33,8 @@ prep_trajectory <- function(data,
                             span_5yr = FALSE,
                             value_col = "percentage_of_initial_production_by_scope") {
 
-  check_prep_trajectory(data, value_col = value_col)
+  env <- list(data = substitute(data))
+  check_prep_trajectory(data, value_col = value_col, env = env)
 
   data <- data %>%
     prep_common() %>%
@@ -47,9 +48,12 @@ prep_trajectory <- function(data,
   data
 }
 
-check_prep_trajectory <- function(data, value_col) {
+check_prep_trajectory <- function(data, value_col, env) {
   stopifnot(is.data.frame(data))
   crucial <- c(common_crucial_market_share_columns(), value_col)
   hint_if_missing_names(abort_if_missing_names(data, crucial), "market_share")
+  enforce_single_value <- c("sector", "technology", "region", "scenario_source")
+  abort_if_multiple(data, enforce_single_value, env = env)
+
   invisible(data)
 }
diff --git a/tests/testthat/test-plot_trajectory.R b/tests/testthat/test-plot_trajectory.R
index 901291f3..d44b2841 100644
--- a/tests/testthat/test-plot_trajectory.R
+++ b/tests/testthat/test-plot_trajectory.R
@@ -41,15 +41,6 @@ test_that("outputs default axis labels", {
   expect_equal(p$labels$y, "value")
 })
 
-test_that("the errors message includes the name of the user's data", {
-  # Keep even if already tested in qplot_. Non-standard evaluation is fragile
-  bad_region <- head(market_share, 2L) %>%
-    mutate(region = c("a", "b")) %>%
-    prep_trajectory()
-
-  expect_error(plot_trajectory(bad_region), "bad_region")
-})
-
 test_that("By default doesn't center the Y axis", {
   data <- example_market_share() %>%
     prep_trajectory(convert_label = identity, span_5yr = FALSE)
diff --git a/tests/testthat/test-prep_trajectory.R b/tests/testthat/test-prep_trajectory.R
index 2267ff5c..b1892b51 100644
--- a/tests/testthat/test-prep_trajectory.R
+++ b/tests/testthat/test-prep_trajectory.R
@@ -44,3 +44,11 @@ test_that("handles span_5yr correctly", {
   out <- prep_trajectory(example_market_share(), span_5yr = TRUE)
   expect_true(all(out$year <= min(out$year) + 5))
 })
+
+test_that("the errors message includes the name of the user's data", {
+  # Keep even if already tested in qplot_. Non-standard evaluation is fragile
+  bad_region <- head(market_share, 2L) %>%
+    mutate(region = c("a", "b"))
+
+  expect_error(prep_trajectory(bad_region), "bad_region")
+})