diff --git a/test/unit/lwip_unittests.c b/test/unit/lwip_unittests.c
index c93f05e2..3cb4a885 100644
--- a/test/unit/lwip_unittests.c
+++ b/test/unit/lwip_unittests.c
@@ -54,7 +54,9 @@ void lwip_check_ensure_no_alloc(unsigned int skip)
   }
   for (i = 0, mask = 1; i < MEMP_MAX; i++, mask <<= 1) {
     if (!(skip & mask)) {
-      fail_unless(lwip_stats.memp[i]->used == 0);
+      fail_unless(lwip_stats.memp[i]->used == 0,
+        "memp pool '%s' still has %d entries allocated",
+        lwip_stats.memp[i]->name, lwip_stats.memp[i]->used);
     }
   }
 }