diff --git a/tests/testthat/test_PredictionSurv.R b/tests/testthat/test_PredictionSurv.R
index d07d53207..ba7ba5171 100644
--- a/tests/testthat/test_PredictionSurv.R
+++ b/tests/testthat/test_PredictionSurv.R
@@ -33,39 +33,55 @@ test_that("c", {
   expect_true(length(times1) == length(times2))
   expect_false(all(times1 == times2))
 
-  # so internal prediction data must be a distribution and not a survival matrix
   pred = do.call(c, preds)
   expect_prediction_surv(pred)
-  expect_class(pred$data$distr, "Distribution")
+  surv_mat = pred$data$distr
+  expect_class(surv_mat, "matrix")
+  # check that time points are properly combined
+  times = as.integer(colnames(surv_mat))
+  expect_true(all(times == sort(union(times1, times2), decreasing = F)))
 
   # data.table conversion
   dt = as.data.table(pred)
   expect_data_table(dt, nrows = task$nrow, ncols = 5L, any.missing = FALSE)
 
   # different number of time points
+  # add extra time point on the 2nd prediction object
   preds2 = rr$predictions()
   preds2[[2]]$data$distr = cbind(distr2,
     matrix(data = rep(0.3, 10), ncol = 1, dimnames = list(NULL, 108)))
-  expect_false(ncol(preds2[[1]]$data$distr) == ncol(preds2[[2]]$data$distr))
+  distr1 = preds2[[1]]$data$distr
+  distr2 = preds2[[2]]$data$distr
+  times1 = as.integer(colnames(distr1))
+  times2 = as.integer(colnames(distr2))
+  expect_false(length(times1) == length(times2))
+
   pred2 = do.call(c, preds2)
   expect_prediction_surv(pred2)
-  expect_class(pred2$data$distr, "Distribution")
+  surv_mat2 = pred2$data$distr
+  expect_class(surv_mat2, "matrix")
+  # check that time points are properly combined
+  times = as.integer(colnames(surv_mat2))
+  expect_true(all(times == sort(union(times1, times2), decreasing = F)))
 
   # combining survival arrays
-  arr_preds = mlr3misc::map(preds, reshape_distr_to_3d)
+  arr_preds = mlr3misc::map(preds2, reshape_distr_to_3d)
   arr_pred = do.call(c, arr_preds)
   expect_prediction_surv(arr_pred)
   expect_class(arr_pred$data$distr, "array")
   expect_class(arr_pred$distr, "Arrdist")
-  # check that time points are combined properly
+  # check that time points are properly combined
+  times1 = as.integer(colnames(arr_preds[[1]]$data$distr))
+  times2 = as.integer(colnames(arr_preds[[2]]$data$distr))
+  times  = as.integer(colnames(arr_pred$data$distr))
   expect_equal(as.integer(colnames(arr_pred$data$distr)),
-    unique(sort(c(times1, times2))))
+    sort(union(times1, times2), decreasing = F))
 
   p1 = lrn("surv.kaplan")$train(task)$predict(task)
   p2 = suppressWarnings(lrn("surv.coxph")$train(task))$predict(task)
   expect_error(c(p1, p2), "Cannot combine")
 
-  # combining distr predictions with exactly the same time points
+  # combining predictions with exactly the same time points
   p1 = lrn("surv.kaplan")$train(task)$predict(task)
   p2 = p1$clone()
   expect_equal(length(c(p1, p2, keep_duplicates = TRUE)$row_ids), 40)
@@ -81,6 +97,55 @@ test_that("c", {
   arr_pred = do.call(c, arr_preds)
   expect_class(arr_pred$data$distr, "array") # combination is an array
   expect_equal(colnames(arr_pred$data$distr), colnames(arr_p1$data$distr)) # same time points
+
+  # combining distr6::Distribution objects of the same type
+  # Matdist
+  p1$data$distr = p1$distr
+  p2$data$distr = p2$distr
+  preds2 = list(p1, p2)
+  pred2 = do.call(c, preds2)
+  expect_class(pred2$data$distr, "matrix")
+  expect_true(all(pred2$data$distr == p12$data$distr))
+
+  # Arrdist
+  arr_p1$data$distr = arr_p1$distr
+  arr_p2$data$distr = arr_p2$distr
+  arr_preds2 = list(arr_p1, arr_p2)
+  arr_pred2 = do.call(c, arr_preds2)
+  expect_class(arr_pred2$data$distr, "array")
+  expect_true(all(arr_pred2$data$distr == arr_pred$data$distr))
+
+  # combining distr6::Distribution objects of different types
+  mix_preds = list(p1, arr_p2) # Matdist and Arrdist
+  expect_error(supressWarnings(do.call(c, mix_preds)))
+
+  # combine survival matrix and Matdist (matrix converts to a Matdist)
+  p1 = lrn("surv.kaplan")$train(task)$predict(task)
+  p2 = p1$clone()
+  p2$data$distr = p2$distr
+  preds = list(p1, p2)
+  expect_prediction_surv(do.call(c, preds))
+
+  # combine survival array and Matdist (array converts to an Arrdist)
+  preds = list(reshape_distr_to_3d(p1), p2)
+  expect_error(do.call(c, preds))
+
+  # combine survival matrix and Arrdist (matrix converts to a Matdist)
+  p2 = p1$clone()
+  p2 = reshape_distr_to_3d(p2)
+  p2$data$distr = p2$distr
+  preds = list(p1, p2)
+  expect_error(supressWarnings(do.call(c, preds)))
+
+  # combine survival array and Arrdist (array converts to an Arrdist)
+  preds = list(reshape_distr_to_3d(p1), p2)
+  expect_prediction_surv(do.call(c, preds))
+
+  # combine survival matrix and array
+  p2 = p1$clone()
+  p2 = reshape_distr_to_3d(p2)
+  preds = list(p1, p2)
+  expect_error(do.call(c, preds), "Cannot combine")
 })
 
 test_that("data.frame roundtrip", {