diff --git a/tests/testthat/test-ppc-errors.R b/tests/testthat/test-ppc-errors.R
index d6424b38..16e8fda0 100644
--- a/tests/testthat/test-ppc-errors.R
+++ b/tests/testthat/test-ppc-errors.R
@@ -4,6 +4,7 @@ context("PPC: predictive errors")
 source(test_path("data-for-ppc-tests.R"))
 
 test_that("ppc_error_hist and ppc_error_scatter return ggplot object", {
+  skip_if_not_installed("rstantools")
   expect_gg(ppc_error_hist(y, yrep[1:5, ], binwidth = 0.1))
   expect_gg(ppc_error_scatter(y, yrep[1:5, ]))
 
@@ -15,17 +16,20 @@ test_that("ppc_error_hist and ppc_error_scatter return ggplot object", {
 })
 
 test_that("ppc_error_hist_grouped returns ggplot object", {
+  skip_if_not_installed("rstantools")
   expect_gg(ppc_error_hist_grouped(y, yrep[1:5, ], group, binwidth = 0.1))
   expect_gg(ppc_error_hist_grouped(y, yrep[1,, drop = FALSE], group,
                                    freq = FALSE, binwidth = 1))
 })
 
 test_that("ppc_error_scatter_avg returns ggplot2 object", {
+  skip_if_not_installed("rstantools")
   expect_gg(ppc_error_scatter_avg(y, yrep))
   expect_gg(ppc_error_scatter_avg(y, yrep[1:5, ]))
 })
 
 test_that("ppc_error_scatter_avg same as ppc_error_scatter if nrow(yrep) = 1", {
+  skip_if_not_installed("rstantools")
   p1 <- ppc_error_scatter_avg(y2, yrep2)
   p2 <- ppc_error_scatter(y2, yrep2)
   d1 <- p1$data
@@ -37,11 +41,13 @@ test_that("ppc_error_scatter_avg same as ppc_error_scatter if nrow(yrep) = 1", {
 })
 
 test_that("ppc_error_scatter_avg_vs_x returns ggplot2 object", {
+  skip_if_not_installed("rstantools")
   expect_gg(ppc_error_scatter_avg_vs_x(y, yrep, x = rnorm(length(y))))
   expect_gg(ppc_error_scatter_avg_vs_x(y, yrep[1:5, ], x = rnorm(length(y))))
 })
 
 test_that("ppc_error_binned returns ggplot object", {
+  skip_if_not_installed("rstantools")
   load(test_path("data-for-binomial.rda"))
   expect_gg(ppc_error_binned(y, Ey))
   expect_gg(ppc_error_binned(y[1:5], Ey[, 1:5]))