diff --git a/inst/include/dust2/r/helpers.hpp b/inst/include/dust2/r/helpers.hpp
index 80447910..dd2db460 100644
--- a/inst/include/dust2/r/helpers.hpp
+++ b/inst/include/dust2/r/helpers.hpp
@@ -124,7 +124,7 @@ std::vector<real_type> check_time_sequence(real_type time_start,
       cpp11::stop("Expected 'time[%d]' to be integer-like", i + 1);
     }
     if (t <= prev) {
-      cpp11::stop("Expected 'time[%d]' (%d) to larger than the previous value (%d)",
+      cpp11::stop("Expected 'time[%d]' (%d) to be larger than the previous value (%d)",
                   i + 1, static_cast<int>(prev), static_cast<int>(t));
     }
     prev = t;
diff --git a/tests/testthat/test-filter.R b/tests/testthat/test-filter.R
index 68e7a28e..88245029 100644
--- a/tests/testthat/test-filter.R
+++ b/tests/testthat/test-filter.R
@@ -64,3 +64,25 @@ test_that("can run run unfilter on structured model", {
   ptr <- obj[[1]]
   expect_equal(dust2_cpu_sir_unfilter_run(ptr, NULL, FALSE), f(pars))
 })
+
+
+test_that("validate time for filter", {
+  pars <- list(beta = 0.1, gamma = 0.2, N = 1000, I0 = 10, exp_noise = 1e6)
+  time_start <- 0
+  time <- as.integer(c(4, 8, 12, 16))
+  data <- lapply(1:4, function(i) list(incidence = i))
+  dt <- 1
+
+  expect_error(
+    dust2_cpu_sir_unfilter_alloc(pars, 5, time, dt, data, 0),
+    "Expected 'time[1]' (5) to be larger than the previous value (4)",
+    fixed = TRUE)
+  expect_error(
+    dust2_cpu_sir_unfilter_alloc(pars, 0, time + c(0, 0, .1, 0), dt, data, 0),
+    "Expected 'time[3]' to be integer-like",
+    fixed = TRUE)
+  expect_error(
+    dust2_cpu_sir_unfilter_alloc(pars, 0, as.character(time), dt, data, 0),
+    "'time' must be a numeric vector",
+    fixed = TRUE)
+})
diff --git a/tests/testthat/test-sir.R b/tests/testthat/test-sir.R
index 53388fc7..1777d0c6 100644
--- a/tests/testthat/test-sir.R
+++ b/tests/testthat/test-sir.R
@@ -96,3 +96,23 @@ test_that("validate data size on compare", {
     dust2_cpu_sir_compare_data(ptr, vector("list", 3), TRUE),
     "'data' must have length 4")
 })
+
+
+test_that("can update parameters", {
+  base <- list(beta = 0.1, gamma = 0.2, N = 1000, I0 = 10, exp_noise = 1e6)
+  update <- list(beta = 0.3, gamma = 0.2)
+  combined <- modifyList(base, update)
+
+  obj1 <- dust2_cpu_sir_alloc(base, 0, 1, 10, 0, 42, FALSE)
+  ptr1 <- obj1[[1]]
+  expect_null(dust2_cpu_sir_update_pars(ptr1, update, FALSE))
+  expect_null(dust2_cpu_sir_run_steps(ptr1, 10))
+
+  obj2 <- dust2_cpu_sir_alloc(combined, 0, 1, 10, 0, 42, FALSE)
+  ptr2 <- obj2[[1]]
+  expect_null(dust2_cpu_sir_run_steps(ptr2, 10))
+
+  expect_equal(
+    dust2_cpu_sir_state(ptr2, FALSE),
+    dust2_cpu_sir_state(ptr1, FALSE))
+})