diff --git a/R/Terminator.R b/R/Terminator.R
index c439d829..f847c9c6 100644
--- a/R/Terminator.R
+++ b/R/Terminator.R
@@ -96,6 +96,7 @@ Terminator = R6Class("Terminator",
     #' time-based, the reaming runtime is `Inf`.
     #' @return `integer(1)`.
     remaining_time = function(archive) {
+      assert_r6(archive, "Archive")
       if (isTRUE(self$unit == "seconds")) {
         status = self$status(archive)
         unname(status["max_steps"] - status["current_steps"])
diff --git a/R/TerminatorClockTime.R b/R/TerminatorClockTime.R
index 37cf0554..25d6aa3b 100644
--- a/R/TerminatorClockTime.R
+++ b/R/TerminatorClockTime.R
@@ -43,6 +43,7 @@ TerminatorClockTime = R6Class("TerminatorClockTime",
     #' otherwise.
     #' @return `logical(1)`.
     is_terminated = function(archive) {
+      assert_r6(archive, "Archive")
       return(Sys.time() >= self$param_set$values$stop_time)
     }
   ),
diff --git a/R/TerminatorCombo.R b/R/TerminatorCombo.R
index a407d6c5..f1acbf1f 100644
--- a/R/TerminatorCombo.R
+++ b/R/TerminatorCombo.R
@@ -56,6 +56,7 @@ TerminatorCombo = R6Class("TerminatorCombo",
     #'
     #' @return `logical(1)`.
     is_terminated = function(archive) {
+      assert_r6(archive, "Archive")
       g = if (self$param_set$values$any) any else all
       g(map_lgl(self$terminators, function(t) t$is_terminated(archive)))
     },
@@ -77,6 +78,7 @@ TerminatorCombo = R6Class("TerminatorCombo",
     #' the the remaining runtime is always `Inf`.
     #' @return `integer(1)`.
     remaining_time = function(archive) {
+      assert_r6(archive, "Archive")
       min_max = if(self$param_set$values$any) min else max
       min_max(map_dbl(self$terminators, function(t) t$remaining_time(archive)), na.rm = TRUE)
     },
@@ -85,6 +87,7 @@ TerminatorCombo = R6Class("TerminatorCombo",
     #' Returns `max_steps` and `current_steps` for each terminator.
     #' @return [data.table::data.table].
     status_long = function(archive) {
+      assert_r6(archive, "Archive")
       map_dtr(self$terminators, function(t) {
         cbind(as.data.table(as.list(t$status(archive))), unit = t$unit)
       })
diff --git a/R/TerminatorEvals.R b/R/TerminatorEvals.R
index f78c9d20..05d4f78a 100644
--- a/R/TerminatorEvals.R
+++ b/R/TerminatorEvals.R
@@ -41,6 +41,7 @@ TerminatorEvals = R6Class("TerminatorEvals",
     #' otherwise.
     #' @return `logical(1)`.
     is_terminated = function(archive) {
+      assert_r6(archive, "Archive")
       archive$n_evals >= self$param_set$values$n_evals
     }
   ),
diff --git a/R/TerminatorNone.R b/R/TerminatorNone.R
index ac763040..df9a4eb7 100644
--- a/R/TerminatorNone.R
+++ b/R/TerminatorNone.R
@@ -30,6 +30,7 @@ TerminatorNone = R6Class("TerminatorNone",
     #' @param archive ([Archive]).
     #' @return `logical(1)`.
     is_terminated = function(archive) {
+      assert_r6(archive, "Archive")
       return(FALSE)
     }
   )
diff --git a/R/TerminatorPerfReached.R b/R/TerminatorPerfReached.R
index 4a819e36..41811e40 100644
--- a/R/TerminatorPerfReached.R
+++ b/R/TerminatorPerfReached.R
@@ -42,6 +42,7 @@ TerminatorPerfReached = R6Class("TerminatorPerfReached",
     #' otherwise.
     #' @return `logical(1)`.
     is_terminated = function(archive) {
+      assert_r6(archive, "Archive")
       level = self$param_set$values$level
       ycol = archive$cols_y
       minimize = "minimize" %in% archive$codomain$tags
diff --git a/R/TerminatorRunTime.R b/R/TerminatorRunTime.R
index 803689f4..9048b16d 100644
--- a/R/TerminatorRunTime.R
+++ b/R/TerminatorRunTime.R
@@ -44,6 +44,7 @@ TerminatorRunTime = R6Class("TerminatorRunTime",
     #' otherwise.
     #' @return `logical(1)`.
     is_terminated = function(archive) {
+      assert_r6(archive, "Archive")
       if(is.null(archive$start_time)) return(FALSE)
       d = as.numeric(difftime(Sys.time(), archive$start_time), units = "secs")
       return(d >= self$param_set$values$secs)
diff --git a/R/TerminatorStagnation.R b/R/TerminatorStagnation.R
index c4dee9fa..f5068a2e 100644
--- a/R/TerminatorStagnation.R
+++ b/R/TerminatorStagnation.R
@@ -46,7 +46,7 @@ TerminatorStagnation = R6Class("TerminatorStagnation",
     #' otherwise.
     #' @return `logical(1)`.
     is_terminated = function(archive) {
-
+      assert_r6(archive, "Archive")
       pv = self$param_set$values
       iters = pv$iters
       ycol = archive$cols_y
diff --git a/R/TerminatorStagnationBatch.R b/R/TerminatorStagnationBatch.R
index e88300c2..188102df 100644
--- a/R/TerminatorStagnationBatch.R
+++ b/R/TerminatorStagnationBatch.R
@@ -46,7 +46,7 @@ TerminatorStagnationBatch = R6Class("TerminatorStagnationBatch",
     #' otherwise.
     #' @return `logical(1)`.
     is_terminated = function(archive) {
-
+      assert_r6(archive, "Archive")
       pv = self$param_set$values
       ycol = archive$cols_y
       present_batch = archive$n_batch