diff --git a/c/tests/test_trees.c b/c/tests/test_trees.c
index 8051c8fe89..497dae7f63 100644
--- a/c/tests/test_trees.c
+++ b/c/tests/test_trees.c
@@ -8258,8 +8258,8 @@ assert_equal_except_edges_and_mutation_nodes(
     ret = tsk_table_collection_copy(ts2->tables, &t2, 0);
     CU_ASSERT_EQUAL_FATAL(ret, 0);
 
-    memset(t1.mutations.node, 0, t1.mutations.num_rows * sizeof(*t1.mutations.node));
-    memset(t2.mutations.node, 0, t2.mutations.num_rows * sizeof(*t2.mutations.node));
+    tsk_memset(t1.mutations.node, 0, t1.mutations.num_rows * sizeof(*t1.mutations.node));
+    tsk_memset(t2.mutations.node, 0, t2.mutations.num_rows * sizeof(*t2.mutations.node));
 
     tsk_edge_table_clear(&t1.edges);
     tsk_edge_table_clear(&t2.edges);