diff --git a/debug_gdn_nan.py b/debug_gdn_nan.py
new file mode 100644
index 00000000..44ed71d6
--- /dev/null
+++ b/debug_gdn_nan.py
@@ -0,0 +1,82 @@
+#!/usr/bin/env python3
+"""Debug NaN in C++ torch_chunk_gated_delta_rule.
+
+Tests with smaller dimensions to isolate the issue.
+"""
+import sys
+import os
+import importlib.util
+import torch
+
+def load_mod():
+    so = "/tmp/gdn_test/corex_gdn_chunk_recurrent.so"
+    if not os.path.exists(so):
+        print("Run verify_gdn_cpp.py first to compile")
+        return None
+    spec = importlib.util.spec_from_file_location("m", so)
+    mod = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(mod)
+    return mod
+
+def main():
+    mod = load_mod()
+    if mod is None:
+        return 1
+
+    # Test with tiny dimensions to isolate
+    for T in [1, 2, 4, 8, 16, 32, 64, 128]:
+        torch.manual_seed(42)
+        B = 1
+        Hk, Hv, D = 4, 8, 128
+        chunk = min(64, T)
+
+        q = torch.randn(B, T, Hk, D, device="cuda", dtype=torch.float16)
+        k = torch.randn(B, T, Hk, D, device="cuda", dtype=torch.float16)
+        v = torch.randn(B, T, Hv, D, device="cuda", dtype=torch.float16)
+        g = torch.randn(B, T, Hv, device="cuda", dtype=torch.float16)
+        beta = torch.randn(B, T, Hv, device="cuda", dtype=torch.float16)
+
+        out, state = mod.torch_chunk_gated_delta_rule(
+            q, k, v, g, beta, chunk, None, True, True)
+
+        has_nan = out.isnan().any().item()
+        nan_count = out.isnan().sum().item() if has_nan else 0
+        print(f"T={T:4d} chunk={chunk:3d}: NaN={has_nan} (count={nan_count}/{out.numel()})")
+
+        if has_nan and T <= 16:
+            # Print where NaN is
+            nan_mask = out.isnan()
+            print(f"  NaN positions: {nan_mask.nonzero()[:5].tolist()}")
+
+    # Test: does chunk_size=T (no actual chunking) work?
+    print("\n--- Single chunk (chunk_size == T) ---")
+    for T in [32, 64]:
+        torch.manual_seed(42)
+        q = torch.randn(1, T, 4, 128, device="cuda", dtype=torch.float16)
+        k = torch.randn(1, T, 4, 128, device="cuda", dtype=torch.float16)
+        v = torch.randn(1, T, 8, 128, device="cuda", dtype=torch.float16)
+        g = torch.randn(1, T, 8, device="cuda", dtype=torch.float16)
+        beta = torch.randn(1, T, 8, device="cuda", dtype=torch.float16)
+
+        out, state = mod.torch_chunk_gated_delta_rule(
+            q, k, v, g, beta, T, None, True, True)
+        print(f"T={T} chunk={T}: NaN={out.isnan().any().item()}")
+
+    # Test: float32 input instead of float16
+    print("\n--- Float32 input ---")
+    for T in [64, 128]:
+        torch.manual_seed(42)
+        q = torch.randn(1, T, 4, 128, device="cuda", dtype=torch.float32)
+        k = torch.randn(1, T, 4, 128, device="cuda", dtype=torch.float32)
+        v = torch.randn(1, T, 8, 128, device="cuda", dtype=torch.float32)
+        g = torch.randn(1, T, 8, device="cuda", dtype=torch.float32)
+        beta = torch.randn(1, T, 8, device="cuda", dtype=torch.float32)
+
+        out, state = mod.torch_chunk_gated_delta_rule(
+            q, k, v, g, beta, 64, None, True, True)
+        print(f"T={T} chunk=64 f32: NaN={out.isnan().any().item()}")
+
+    return 0
+
+if __name__ == "__main__":
+    sys.exit(main())