diff --git a/crates/model/tests/attn.rs b/crates/model/tests/attn.rs
index 0adbb44dc..59ebe4c7f 100644
--- a/crates/model/tests/attn.rs
+++ b/crates/model/tests/attn.rs
@@ -237,14 +237,6 @@ fn hw_attn_exact_input_stages() {
             v,
         )
     };
-    let maxdiff = |a: &Tensor2, b: &Tensor2| {
-        a.data
-            .iter()
-            .zip(&b.data)
-            .map(|(x, y)| (x - y).abs())
-            .fold(0.0f32, f32::max)
-    };
-
     for blk in [0usize, 1usize] {
         let g = gguf::Gguf::open(model_path::model_path()).unwrap();
         let p = attn::MlaParams::read(&g, blk).unwrap();
@@ -262,9 +254,11 @@ fn hw_attn_exact_input_stages() {
             attn::q_nope2_absorbed(derived.wk_b_all_heads(blk).unwrap(), &q_exact, &p).unwrap();
         let want = load2(&format!("q_nope2-{blk}"), 0);
         assert_eq!([out.ne0, out.ne1], [want.ne0, want.ne1], "stage A shape");
-        assert!(
-            maxdiff(&out, &want) <= 1e-5,
-            "stage A: absorption arithmetic"
+        asserts::assert_close(
+            &out.data,
+            &want.data,
+            1e-5,
+            "stage A: absorption arithmetic",
         );
 
         // B: the attention proper — two legs.
@@ -366,9 +360,11 @@ fn hw_attn_exact_input_stages() {
         let out = model::ops::matmul_q(&g, wo, &kqv_2d).unwrap();
         let want = load2(&format!("kqv_out-{blk}"), 0);
         assert_eq!([out.ne0, out.ne1], [want.ne0, want.ne1], "stage C shape");
-        assert!(
-            maxdiff(&out, &want) <= 1e-4,
-            "stage C: wv_b + output projection"
+        asserts::assert_close(
+            &out.data,
+            &want.data,
+            1e-4,
+            "stage C: wv_b + output projection",
         );
     }
 }
diff --git a/crates/model/tests/common/asserts.rs b/crates/model/tests/common/asserts.rs
index 518cfb742..4d2d55c77 100644
--- a/crates/model/tests/common/asserts.rs
+++ b/crates/model/tests/common/asserts.rs
@@ -13,6 +13,15 @@ pub fn assert_close(got: &[f32], want: &[f32], tol: f32, what: &str) {
     let mut worst = 0.0f32;
     let mut at = 0usize;
     for (i, (&g, &w)) in got.iter().zip(want).enumerate() {
+        // Reject non-finite operands before comparing errors.
+        assert!(
+            g.is_finite(),
+            "{what}: non-finite got at index {i} (reference {w}); gate is {tol:e}"
+        );
+        assert!(
+            w.is_finite(),
+            "{what}: non-finite reference at index {i} (got {g}); gate is {tol:e}"
+        );
         let d = (g - w).abs();
         if d > worst {
             worst = d;
diff --git a/crates/model/tests/derived.rs b/crates/model/tests/derived.rs
index 61412ed29..5ef62239b 100644
--- a/crates/model/tests/derived.rs
+++ b/crates/model/tests/derived.rs
@@ -24,6 +24,8 @@
 //! `hw_` prefix: needs the box and the model file. Like `tests/kv.rs`, this
 //! compares our paths against each other — `tests/attn.rs` and
 //! `tests/forward.rs` are what tie them to ik.
+#[path = "common/asserts.rs"]
+mod asserts;
 #[path = "common/manifest.rs"]
 mod manifest;
 #[path = "common/model_path.rs"]
@@ -119,15 +121,11 @@ fn hw_derived_wblocks_bit_identical() {
         let from_reference = q_nope2_absorbed(&reference_flat, &q, &p).unwrap();
         let from_derived = q_nope2_absorbed(d.wk_b_all_heads(blk).unwrap(), &q, &p).unwrap();
         assert_eq!(from_derived.data.len(), from_reference.data.len(), "shape");
-        let worst = from_derived
-            .data
-            .iter()
-            .zip(&from_reference.data)
-            .map(|(&a, &b)| (a - b).abs())
-            .fold(0.0f32, f32::max);
-        assert_eq!(
-            worst, 0.0,
-            "q_nope2-{blk}: cached-wblocks vs in-place-wblocks max|diff| {worst:e}"
+        asserts::assert_close(
+            &from_derived.data,
+            &from_reference.data,
+            0.0,
+            &format!("q_nope2-{blk}: cached-wblocks vs in-place-wblocks"),
         );
         eprintln!("q_nope2-{blk:<4} cached == in-place   max|diff| = 0   exact");
     }
diff --git a/crates/model/tests/forward.rs b/crates/model/tests/forward.rs
index 8ca41fdb2..12eac92b0 100644
--- a/crates/model/tests/forward.rs
+++ b/crates/model/tests/forward.rs
@@ -28,6 +28,10 @@ fn max_abs_diff(got: &[f32], want: &[f32]) -> (f32, usize) {
     let mut worst = 0.0f32;
     let mut at = 0usize;
     for (i, (&g, &w)) in got.iter().zip(want).enumerate() {
+        assert!(
+            g.is_finite() && w.is_finite(),
+            "non-finite comparison operand at index {i}: got {g}, reference {w}"
+        );
         let d = (g - w).abs();
         if d > worst {
             worst = d;
diff --git a/crates/model/tests/head.rs b/crates/model/tests/head.rs
index 21ae18732..0c35fa3d1 100644
--- a/crates/model/tests/head.rs
+++ b/crates/model/tests/head.rs
@@ -63,6 +63,10 @@ fn assert_close_rel(got: &[f32], want: &[f32], what: &str) {
     let mut at = 0usize;
     let mut pair = (0.0f32, 0.0f32);
     for (i, (&g, &w)) in got.iter().zip(want).enumerate() {
+        assert!(
+            g.is_finite() && w.is_finite(),
+            "non-finite comparison operand at index {i}: got {g}, reference {w}"
+        );
         let d = (g - w).abs();
         worst_abs = worst_abs.max(d);
         max_abs_ref = max_abs_ref.max(w.abs());
diff --git a/crates/model/tests/kv.rs b/crates/model/tests/kv.rs
index 3ca6fb3f5..f904a952c 100644
--- a/crates/model/tests/kv.rs
+++ b/crates/model/tests/kv.rs
@@ -34,7 +34,14 @@ fn max_abs_diff(got: &[f32], want: &[f32]) -> f32 {
     );
     got.iter()
         .zip(want)
-        .map(|(&g, &w)| (g - w).abs())
+        .enumerate()
+        .map(|(i, (&g, &w))| {
+            assert!(
+                g.is_finite() && w.is_finite(),
+                "non-finite comparison operand at index {i}: got {g}, reference {w}"
+            );
+            (g - w).abs()
+        })
         .fold(0.0f32, f32::max)
 }
 
@@ -43,8 +50,8 @@ fn max_abs_diff(got: &[f32], want: &[f32]) -> f32 {
 /// only its batch, so any difference here means the shim is not the identity it says
 /// it is. The same run is `Derived`'s end-to-end claim (`tests/derived.rs`, layer 3):
 /// `forward` builds its own `Derived`, `step` is handed one, and block `b`'s absorption
-/// must get block `b`'s blocks either way. Bits, not differences: `NaN - NaN` folds to
-/// a clean zero through `f32::max`.
+/// must get block `b`'s blocks either way. Bits, not differences; a non-finite
+/// side in either vector is refused before the fold.
 #[test]
 #[ignore = "hw: needs the box and the model file"]
 fn hw_kv_one_shot_equals_uncached() {
diff --git a/crates/model/tests/ops.rs b/crates/model/tests/ops.rs
index 9c52042e2..a098c85bf 100644
--- a/crates/model/tests/ops.rs
+++ b/crates/model/tests/ops.rs
@@ -51,6 +51,23 @@ fn hw_rms_norm_matches_ggml() {
     asserts::assert_close(&got.data, &want, 0.0, "rms_norm -> attn_norm-0");
 }
 
+// The shared numeric gate rejects a non-finite output without fixtures.
+#[test]
+fn the_nan_output_cell_cannot_pass_the_gate() {
+    let got = std::panic::catch_unwind(|| {
+        asserts::assert_close(&[f32::NAN], &[1.0], 0.0, "rms_norm mutant -> attn_norm-0")
+    })
+    .is_err();
+    let reference = std::panic::catch_unwind(|| {
+        asserts::assert_close(&[1.0], &[f32::NAN], 0.0, "rms_norm mutant -> attn_norm-0")
+    })
+    .is_err();
+    assert!(
+        got && reference,
+        "a NaN must fail the gate in each operand position"
+    );
+}
+
 #[test]
 #[ignore = "hw: needs the box, the model file and $BLOOMERY_DATA/ref"]
 fn hw_matmul_q_matches_ggml() {
diff --git a/crates/model/tests/profile.rs b/crates/model/tests/profile.rs
index a78360729..6516d7725 100644
--- a/crates/model/tests/profile.rs
+++ b/crates/model/tests/profile.rs
@@ -24,6 +24,8 @@
 //! hold anything specific — the oracle is used only as the shared prompt, the same
 //! one every other gate runs, so the bit-identity claim is about the prompt that
 //! matters.
+#[path = "common/asserts.rs"]
+mod asserts;
 #[path = "common/manifest.rs"]
 mod manifest;
 #[path = "common/model_path.rs"]
@@ -117,17 +119,7 @@ fn hw_profile_gate() {
         off.len(),
         on.len()
     );
-    let worst = off
-        .iter()
-        .zip(&on)
-        .map(|(&a, &b)| (a - b).abs())
-        .fold(0.0f32, f32::max);
-    assert_eq!(
-        worst,
-        0.0,
-        "profiling changed the logits: max|diff| {worst:e} over {} values",
-        off.len()
-    );
+    asserts::assert_close(&on, &off, 0.0, "profiling changed the logits");
     eprintln!("logits, off vs profiled level 2      max|diff| = 0   exact");
 
     // Assertions 2 and 3 need the in-process accumulators. The children were separate