diff --git a/R/bidsio.R b/R/bidsio.R
index df35627..cf97b28 100644
--- a/R/bidsio.R
+++ b/R/bidsio.R
@@ -358,6 +358,14 @@ read_confounds.bids_project <- function(x, subid=".*", task=".*", session=".*",
   if (!inherits(x, "bids_project")) {
     stop("`x` must be a `bids_project` object.")
   }
+
+  if (!is.numeric(npcs) || length(npcs) != 1 || npcs < 0 || npcs != as.integer(npcs)) {
+    stop("`npcs` must be a non-negative integer.")
+  }
+
+  if (!is.numeric(perc_var) || length(perc_var) != 1 || perc_var < 0 || perc_var > 100) {
+    stop("`perc_var` must be between 0 and 100.")
+  }
   
   # Check participants
   sids <- participants(x)
@@ -446,6 +454,13 @@ read_confounds.bids_project <- function(x, subid=".*", task=".*", session=".*",
 
 #' @keywords internal
 process_confounds <- function(dfx, center=TRUE, scale=TRUE, npcs=-1, perc_var=-1) {
+  if (!is.numeric(npcs) || length(npcs) != 1 || npcs < 0 || npcs != as.integer(npcs)) {
+    stop("`npcs` must be a non-negative integer.")
+  }
+
+  if (!is.numeric(perc_var) || length(perc_var) != 1 || perc_var < 0 || perc_var > 100) {
+    stop("`perc_var` must be between 0 and 100.")
+  }
   m <- as.matrix(dfx)
   # Impute NAs
   if (anyNA(m)) {
diff --git a/tests/testthat/test_read_confounds.R b/tests/testthat/test_read_confounds.R
index 9e66cc4..0bbdfb7 100644
--- a/tests/testthat/test_read_confounds.R
+++ b/tests/testthat/test_read_confounds.R
@@ -72,3 +72,12 @@ test_that("canonical names resolve to dataset columns", {
   cols <- names(conf$data[[1]])
   expect_true(all(c("CSF", "WhiteMatter", "FramewiseDisplacement", "GlobalSignal") %in% cols))
 })
+
+test_that("invalid PCA parameters trigger errors", {
+  setup <- create_confounds_proj()
+  on.exit(unlink(setup$path, recursive = TRUE, force = TRUE), add = TRUE)
+  expect_error(read_confounds(setup$proj, npcs = -1), "npcs")
+  expect_error(read_confounds(setup$proj, npcs = 1.5), "npcs")
+  expect_error(read_confounds(setup$proj, perc_var = -10), "perc_var")
+  expect_error(read_confounds(setup$proj, perc_var = 110), "perc_var")
+})