diff --git a/cpp/test/neighbors/ann_ivf_pq.cuh b/cpp/test/neighbors/ann_ivf_pq.cuh
index bb6fb30ad3..9d6ad11ccb 100644
--- a/cpp/test/neighbors/ann_ivf_pq.cuh
+++ b/cpp/test/neighbors/ann_ivf_pq.cuh
@@ -35,6 +35,8 @@
 
 #include <gtest/gtest.h>
 
+#include <cub/cub.cuh>
+#include <thrust/reduce.h>
 #include <thrust/sequence.h>
 
 #include <algorithm>
@@ -106,6 +108,18 @@ inline auto operator<<(std::ostream& os, const ivf_pq_inputs& p) -> std::ostream
   return os;
 }
 
+template <typename IdxT>
+auto min_output_size(const handle_t& handle, const ivf_pq::index<IdxT>& index, uint32_t n_probes)
+  -> IdxT
+{
+  uint32_t skip = index.n_nonempty_lists() > n_probes ? index.n_nonempty_lists() - n_probes : 0;
+  auto map_type = [] __device__(uint32_t x) { return IdxT(x); };
+  using iter    = cub::TransformInputIterator<IdxT, decltype(map_type), const uint32_t*>;
+  iter start(index.list_sizes().data_handle() + skip, map_type);
+  iter end(index.list_sizes().data_handle() + index.n_nonempty_lists(), map_type);
+  return thrust::reduce(handle.get_thrust_policy(), start, end);
+}
+
 template <typename EvalT, typename DataT, typename IdxT>
 class ivf_pq_test : public ::testing::TestWithParam<ivf_pq_inputs> {
  public:
@@ -189,7 +203,7 @@ class ivf_pq_test : public ::testing::TestWithParam<ivf_pq_inputs> {
   }
 
   template <typename BuildIndex>
-  auto run(BuildIndex build_index)
+  void run(BuildIndex build_index)
   {
     auto index = build_index();
 
@@ -228,6 +242,39 @@ class ivf_pq_test : public ::testing::TestWithParam<ivf_pq_inputs> {
                                 ps.k,
                                 0.001 / low_precision_factor,
                                 min_recall));
+
+    // Test a few extra invariants
+    IdxT min_results = min_output_size(handle_, index, ps.search_params.n_probes);
+    IdxT max_oob     = ps.k <= min_results ? 0 : ps.k - min_results;
+    IdxT found_oob   = 0;
+    for (uint32_t query_ix = 0; query_ix < ps.num_queries; query_ix++) {
+      for (uint32_t k = 0; k < ps.k; k++) {
+        auto flat_i   = query_ix * ps.k + k;
+        auto found_ix = indices_ivf_pq[flat_i];
+        if (found_ix == ivf_pq::index<IdxT>::kOutOfBoundsRecord) {
+          found_oob++;
+          continue;
+        }
+        ASSERT_NE(found_ix, ivf_pq::index<IdxT>::kInvalidRecord)
+          << "got an invalid record at query_ix = " << query_ix << ", k = " << k
+          << " (distance = " << distances_ivf_pq[flat_i] << ")";
+        ASSERT_LT(found_ix, ps.num_db_vecs)
+          << "got an impossible index = " << found_ix << " at query_ix = " << query_ix
+          << ", k = " << k << " (distance = " << distances_ivf_pq[flat_i] << ")";
+      }
+    }
+    ASSERT_LE(found_oob, max_oob)
+      << "got too many records out-of-bounds (see ivf_pq::index<IdxT>::kOutOfBoundsRecord).";
+    if (found_oob > 0) {
+      RAFT_LOG_WARN(
+        "Got %zu results out-of-bounds because of large top-k (%zu) and small n_probes (%u) and "
+        "small DB size/n_lists ratio (%zu / %u)",
+        size_t(found_oob),
+        size_t(ps.k),
+        ps.search_params.n_probes,
+        size_t(ps.num_db_vecs),
+        ps.index_params.n_lists);
+    }
   }
 
   void SetUp() override  // NOLINT