diff --git a/cpp/src/neighbors/detail/cagra/cagra_build.cuh b/cpp/src/neighbors/detail/cagra/cagra_build.cuh
index a7c15b4161..98fbfc002c 100644
--- a/cpp/src/neighbors/detail/cagra/cagra_build.cuh
+++ b/cpp/src/neighbors/detail/cagra/cagra_build.cuh
@@ -69,6 +69,17 @@ void check_graph_degree(size_t& intermediate_degree, size_t& graph_degree, size_
       intermediate_degree);
     graph_degree = intermediate_degree;
   }
+
+  const size_t recommended_intermediate = recommended_intermediate_graph_degree(graph_degree);
+  if (intermediate_degree < recommended_intermediate) {
+    RAFT_LOG_WARN(
+      "CAGRA: intermediate_graph_degree (%lu) is below the recommended minimum (%lu, i.e. "
+      "1.5 * graph_degree). Pruning to graph_degree (%lu) may result in a disconnected graph"
+      " if the intermediate graph does not retain enough neighborhood information.",
+      intermediate_degree,
+      recommended_intermediate,
+      graph_degree);
+  }
 }
 
 // ACE: Get partition labels for partitioned approach
diff --git a/cpp/src/neighbors/detail/cagra/graph_core.cuh b/cpp/src/neighbors/detail/cagra/graph_core.cuh
index 52b4542798..e7e9842d27 100644
--- a/cpp/src/neighbors/detail/cagra/graph_core.cuh
+++ b/cpp/src/neighbors/detail/cagra/graph_core.cuh
@@ -1676,11 +1676,19 @@ void prune_graph_gpu(
   raft::copy(res, host_stats.view(), raft::make_const_mdspan(dev_stats.view()));
   raft::resource::sync_stream(res);
 
+  const size_t recommended_intermediate =
+    recommended_intermediate_graph_degree(output_graph_degree);
   RAFT_EXPECTS(
     invalid_neighbor_list == 0,
-    "Could not generate an intermediate CAGRA graph because the initial kNN graph contains too "
-    "many invalid or duplicated neighbor nodes. This error can occur, for example, if too many "
-    "overflows occur during the norm computation between the dataset vectors.");
+    "CAGRA graph pruning failed: could not select graph_degree (%lu) distinct neighbors for "
+    "every node from the intermediate kNN graph (intermediate_graph_degree=%lu). This usually "
+    "means the intermediate graph does not encode enough neighborhood information for pruning — "
+    "for example when intermediate_graph_degree is too close to graph_degree. Set "
+    "intermediate_graph_degree >= %lu (1.5 * graph_degree). "
+    "Other causes include invalid or duplicate neighbor indices in the intermediate kNN graph.",
+    output_graph_degree,
+    knn_graph_degree,
+    recommended_intermediate);
 
   num_keep = host_stats.data_handle()[0];
   num_full = host_stats.data_handle()[1];
diff --git a/cpp/src/neighbors/detail/cagra/utils.hpp b/cpp/src/neighbors/detail/cagra/utils.hpp
index 58bf68bb43..7f0c516db2 100644
--- a/cpp/src/neighbors/detail/cagra/utils.hpp
+++ b/cpp/src/neighbors/detail/cagra/utils.hpp
@@ -301,4 +301,9 @@ void copy_with_padding(
   }
 }
 
+constexpr size_t recommended_intermediate_graph_degree(size_t graph_degree) noexcept
+{
+  return graph_degree + ((graph_degree + 1) / 2);
+}
+
 }  // namespace cuvs::neighbors::cagra::detail