diff --git a/cpptests/test_fixation_pruning_during_simulation.cc b/cpptests/test_fixation_pruning_during_simulation.cc
index 7485b1a9d..664db9bab 100644
--- a/cpptests/test_fixation_pruning_during_simulation.cc
+++ b/cpptests/test_fixation_pruning_during_simulation.cc
@@ -159,6 +159,7 @@ BOOST_FIXTURE_TEST_CASE(test_retain_fixations, common_setup)
     BOOST_REQUIRE_EQUAL(pop.generation, 1000);
     BOOST_REQUIRE_EQUAL(pop.fixations.size(), pop.fixation_times.size());
     BOOST_REQUIRE(!pop.fixations.empty());
+    BOOST_REQUIRE(pop.fixations.size() > 1);
     for (const auto &g : pop.haploid_genomes)
         {
             if (g.n > 0)