diff --git a/test/regress_buffer.c b/test/regress_buffer.c
index 4f4a8303..327210b0 100644
--- a/test/regress_buffer.c
+++ b/test/regress_buffer.c
@@ -1140,7 +1140,9 @@ test_evbuffer_callbacks(void *ptr)
 	evbuffer_drain(buf_out2, evbuffer_get_length(buf_out2));
 	/* Let's test the obsolete buffer_setcb function too. */
 	cb1 = evbuffer_add_cb(buf, log_change_callback, buf_out1);
+	tt_assert(cb1 != NULL);
 	cb2 = evbuffer_add_cb(buf, log_change_callback, buf_out2);
+	tt_assert(cb2 != NULL);
 	evbuffer_setcb(buf, self_draining_callback, NULL);
 	evbuffer_add_printf(buf, "This should get drained right away.");
 	tt_uint_op(evbuffer_get_length(buf), ==, 0);