diff --git a/families/personaplex/default_dual_profile_decoder.py b/families/personaplex/default_dual_profile_decoder.py
index 19fca8d359..0221ea3270 100644
--- a/families/personaplex/default_dual_profile_decoder.py
+++ b/families/personaplex/default_dual_profile_decoder.py
@@ -83,12 +83,8 @@ def _swiglu_mlp(
 ) -> trt.ITensor:
     gate = matmul(inp, hidden, mlp_size, weights[f"{prefix}.w_gate"], f"{prefix}.w_gate")
     up = matmul(inp, hidden, mlp_size, weights[f"{prefix}.w_up"], f"{prefix}.w_up")
-    sigmoid = network.add_activation(gate, trt.ActivationType.SIGMOID)
-    swish = network.add_elementwise(gate, sigmoid.get_output(0), trt.ElementWiseOperation.PROD)
-    gated = network.add_elementwise(swish.get_output(0), up, trt.ElementWiseOperation.PROD)
-    mlp_out = matmul(
-        gated.get_output(0), mlp_size, hidden, weights[f"{prefix}.w_down"], f"{prefix}.w_down"
-    )
+    gated = graph_blocks.add_swiglu_activation(network, gate, up)
+    mlp_out = matmul(gated, mlp_size, hidden, weights[f"{prefix}.w_down"], f"{prefix}.w_down")
     return mlp_out
 
 
diff --git a/families/personaplex/graph_blocks.py b/families/personaplex/graph_blocks.py
index 2fc6187026..e81d482606 100644
--- a/families/personaplex/graph_blocks.py
+++ b/families/personaplex/graph_blocks.py
@@ -313,6 +313,27 @@ def add_attention_block(
     }
 
 
+def add_swiglu_activation(
+    network: trt.INetworkDefinition, gate: trt.ITensor, up: trt.ITensor
+) -> trt.ITensor:
+    """SiLU(gate) * up in FP32, rounded once to the projections' dtype.
+
+    The reference gating kernel computes the activation and the product in FP32
+    from Half/BF16 projections and rounds only the result; rounding SiLU(gate)
+    first changes the product.
+    """
+    work_dtype = gate.dtype
+    if work_dtype != trt.float32:
+        gate = network.add_cast(gate, trt.float32).get_output(0)
+        up = network.add_cast(up, trt.float32).get_output(0)
+    sigmoid = network.add_activation(gate, trt.ActivationType.SIGMOID).get_output(0)
+    swish = network.add_elementwise(gate, sigmoid, trt.ElementWiseOperation.PROD).get_output(0)
+    gated = network.add_elementwise(swish, up, trt.ElementWiseOperation.PROD).get_output(0)
+    if work_dtype != trt.float32:
+        gated = network.add_cast(gated, work_dtype).get_output(0)
+    return gated
+
+
 def add_swiglu_mlp(
     network: trt.INetworkDefinition,
     inp: trt.ITensor,
@@ -332,13 +353,9 @@ def add_swiglu_mlp(
     gate = matmul(inp, hidden_size, mlp_size, weights[f"{prefix}.w_gate"], f"{_lp}.w_gate")
     up = matmul(inp, hidden_size, mlp_size, weights[f"{prefix}.w_up"], f"{_lp}.w_up")
 
-    sigmoid = network.add_activation(gate, trt.ActivationType.SIGMOID)
-    swish = network.add_elementwise(gate, sigmoid.get_output(0), trt.ElementWiseOperation.PROD)
-    gated = network.add_elementwise(swish.get_output(0), up, trt.ElementWiseOperation.PROD)
+    gated = add_swiglu_activation(network, gate, up)
 
-    mlp_out = matmul(
-        gated.get_output(0), mlp_size, hidden_size, weights[f"{prefix}.w_down"], f"{_lp}.w_down"
-    )
+    mlp_out = matmul(gated, mlp_size, hidden_size, weights[f"{prefix}.w_down"], f"{_lp}.w_down")
     return mlp_out
 
 
diff --git a/families/personaplex/tests/test_swiglu_precision.py b/families/personaplex/tests/test_swiglu_precision.py
new file mode 100644
index 0000000000..14e0faf8b0
--- /dev/null
+++ b/families/personaplex/tests/test_swiglu_precision.py
@@ -0,0 +1,95 @@
+# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+"""Exercise the SwiGLU rounding boundary through the MLP's normal output."""
+
+import numpy as np
+import pytest
+
+trt = pytest.importorskip("tensorrt")
+torch = pytest.importorskip("torch")
+
+from families.personaplex import graph_blocks  # noqa: E402
+from families.personaplex.default_dual_profile_decoder import _swiglu_mlp  # noqa: E402
+
+WIDTH = 128
+# Binary values: exact in Half and BF16. Rounding SiLU(gate) to Half before the
+# product gives 0.0865478515625; the FP32 product rounded once gives
+# 0.08648681640625, about 600 FP32 ulps from a Half rounding boundary.
+GATE, UP = 7.0 / 64.0, 1.5
+
+
+def _weights():
+    # One-hot input selects row 0; each projection has a single unit path, so
+    # every GEMM output is exact and only the activation boundary can differ.
+    w_gate = np.zeros((WIDTH, WIDTH), np.float32)
+    w_up = np.zeros((WIDTH, WIDTH), np.float32)
+    w_down = np.zeros((WIDTH, WIDTH), np.float32)
+    w_gate[0, 0], w_up[0, 0], w_down[0, 0] = GATE, UP, 1.0
+    return {"mlp.w_gate": w_gate, "mlp.w_up": w_up, "mlp.w_down": w_down}
+
+
+def _build(path):
+    logger = trt.Logger(trt.Logger.ERROR)
+    builder = trt.Builder(logger)
+    network = builder.create_network(1 << int(trt.NetworkDefinitionCreationFlag.STRONGLY_TYPED))
+    x = network.add_input("x", trt.float16, (1, WIDTH))
+    weights = _weights()
+    if path == "graph_blocks":
+        y = graph_blocks.add_swiglu_mlp(
+            network,
+            x,
+            weights=weights,
+            prefix="mlp",
+            hidden_size=WIDTH,
+            mlp_size=WIDTH,
+            dtype=np.float16,
+        )
+    else:
+        matmul = graph_blocks.make_matmul_fn(network, np.float16, None)
+        y = _swiglu_mlp(
+            network,
+            x,
+            matmul=matmul,
+            weights=weights,
+            prefix="mlp",
+            hidden=WIDTH,
+            mlp_size=WIDTH,
+        )
+    y.name = "y"
+    network.mark_output(y)
+    config = builder.create_builder_config()
+    plan = builder.build_serialized_network(network, config)
+    assert plan is not None
+    runtime = trt.Runtime(logger)
+    return runtime, runtime.deserialize_cuda_engine(plan)
+
+
+@pytest.mark.gpu
+@pytest.mark.trt
+@pytest.mark.parametrize("rebuild", range(3))
+@pytest.mark.parametrize("path", ["graph_blocks", "dual_profile"])
+def test_swiglu_rounds_the_product_once(path, rebuild):
+    if not torch.cuda.is_available():
+        pytest.skip("CUDA is required")
+    del rebuild  # Each parametrized invocation builds a separate engine.
+    runtime, engine = _build(path)
+    assert engine is not None
+    context = engine.create_execution_context()
+    assert context is not None
+    x = torch.zeros((1, WIDTH), dtype=torch.float16, device="cuda")
+    x[0, 0] = 1.0
+    y = torch.empty((1, WIDTH), dtype=torch.float16, device="cuda")
+    assert context.set_tensor_address("x", x.data_ptr())
+    assert context.set_tensor_address("y", y.data_ptr())
+    assert context.execute_async_v3(torch.cuda.current_stream().cuda_stream)
+    torch.cuda.synchronize()
+    actual = y.cpu().reshape(-1)
+    del context, engine, runtime
+    # Pinned Moshi's compiled gating kernel: Half projections, SiLU and the
+    # product in FP32, then one conversion to Half.
+    gate = torch.tensor(GATE, dtype=torch.float32, device="cuda")
+    up = torch.tensor(UP, dtype=torch.float32, device="cuda")
+    expected = torch.zeros(WIDTH, dtype=torch.float16)
+    expected[0] = (torch.nn.functional.silu(gate) * up).half().cpu()
+    torch.testing.assert_close(actual, expected, rtol=0, atol=0)