diff --git a/single_shot_inference.py b/single_shot_inference.py
index e3c91ce6..224c634d 100644
--- a/single_shot_inference.py
+++ b/single_shot_inference.py
@@ -455,7 +455,8 @@ class KVCache:
         # P3: Pre-allocate compressed KV buffers (no more torch.cat / O(N²) growth)
         self.comp_kv_buf = torch.zeros(max_comp, head_dim, dtype=torch.bfloat16, device=device)
         self.comp_pos_buf = torch.zeros(max_comp, dtype=torch.long, device=device)
-        self.comp_idx_buf = torch.zeros(max_comp, head_dim, dtype=torch.bfloat16, device=device)
+        # Indexer compressed keys are width ihd (128), NOT head_dim (512)
+        self.comp_idx_buf = torch.zeros(max_comp, 128, dtype=torch.bfloat16, device=device)  # PROBE: width=ihd
         self.n_comp = 0
         self._has_idx = False