diff --git a/R/drug_parameters.R b/R/drug_parameters.R
index f5e62a27..4f205604 100644
--- a/R/drug_parameters.R
+++ b/R/drug_parameters.R
@@ -24,6 +24,7 @@ SP_AQ_params <- c(0.9, 0.32, 4.3, 38.1)
 #' @param drugs a list of drug parameters, can be set using presets
 #' @export
 set_drugs <- function(parameters, drugs) {
+  stopifnot(is.list(drugs))
   keys <- c(
     'drug_efficacy',
     'drug_rel_c',
diff --git a/tests/testthat/test-treatment.R b/tests/testthat/test-treatment.R
index d52fc007..9e40c0da 100644
--- a/tests/testthat/test-treatment.R
+++ b/tests/testthat/test-treatment.R
@@ -78,3 +78,12 @@ test_that('You cannot set invalid coverages', {
     )
   )
 })
+
+test_that('set_drugs errors if a list is not provided', {
+  parameters <- get_parameters()
+  expect_error(
+    set_drugs(parameters, AL_params),
+    "is.list(drugs) is not TRUE",
+    fixed = TRUE
+  )
+})