diff --git a/cub/agent/agent_scan.cuh b/cub/agent/agent_scan.cuh
index e8869034c..ccac7f596 100644
--- a/cub/agent/agent_scan.cuh
+++ b/cub/agent/agent_scan.cuh
@@ -358,7 +358,7 @@ struct AgentScan
 
     // Wait for all threads in the cluster to finish loading / dsmem initialization
     cooperative_groups::cluster_group::barrier_wait(std::move(token));
-    // CTA_SYNC();
+    CTA_SYNC(); // What, this sync fixes the race
 
     // Perform tile scan
     if (tile_idx == 0)
diff --git a/cub/agent/single_pass_scan_operators.cuh b/cub/agent/single_pass_scan_operators.cuh
index c8fae92af..ddf90af5b 100644
--- a/cub/agent/single_pass_scan_operators.cuh
+++ b/cub/agent/single_pass_scan_operators.cuh
@@ -593,6 +593,8 @@ struct ClusterTilePrefixCallbackOp
                 }
                 exclusive_prefix = Reduce(cta_rank, src_cta, tile_descriptor.value);
 
+                // second thread of block 31 reads 2399 instead of 1920
+
                 if (__shfl_sync(CUB_DETAIL_CLUSTER_WARP_MASK,
                                 tile_descriptor.status == SCAN_TILE_PARTIAL,
                                 0,