diff --git a/ptx/lib/zluda_ptx_impl.cpp b/ptx/lib/zluda_ptx_impl.cpp
--- a/ptx/lib/zluda_ptx_impl.cpp
+++ b/ptx/lib/zluda_ptx_impl.cpp
@@ -877,21 +877,18 @@
         typedef _Float16 half_vector __attribute__((ext_vector_type(2)));
         typedef uint16_t magnitude_vector __attribute__((ext_vector_type(2)));
         const uint32_t bits = std::bit_cast<uint32_t>(input);
-        // Positive half encodings are ordered by magnitude. Clamp both lanes
-        // with one packed integer min, then retain NaNs as positive quiet NaNs.
-        // Restore original signs after conversion, including negative zero.
         const magnitude_vector magnitude = std::bit_cast<magnitude_vector>(bits & 0x7fff7fffu);
-        const magnitude_vector saturated =
+        // Clamp finite overflow and infinities explicitly. Map NaNs to signed
+        // infinity: native infinity encodes as 0x7f/0xff, whereas native NaN is
+        // always 0xff. This preserves the sign without post-conversion masks.
+        const magnitude_vector bounded =
             __builtin_elementwise_min(magnitude, magnitude_vector{0x5f00u, 0x5f00u});
         const magnitude_vector kept{
-            magnitude[0] > 0x7c00u ? uint16_t(0x7e00u) : saturated[0],
-            magnitude[1] > 0x7c00u ? uint16_t(0x7e00u) : saturated[1]};
-        const half_vector halves = std::bit_cast<half_vector>(kept);
-        const float x = float(halves[0]), y = float(halves[1]);
-        const uint32_t encoded = d4r_cvt_pk_fp8_f32(x, y, 0, false);
-        // AMD canonicalizes NaNs to 0xff. PTX retains each input's sign.
-        const uint16_t packed = uint16_t((encoded & 0x7f7fu) |
-                                        ((bits >> 8) & 0x80u) | ((bits >> 16) & 0x8000u));
+            magnitude[0] > 0x7c00u ? uint16_t(0x7c00u) : bounded[0],
+            magnitude[1] > 0x7c00u ? uint16_t(0x7c00u) : bounded[1]};
+        const uint32_t signed_bits = std::bit_cast<uint32_t>(kept) | (bits & 0x80008000u);
+        const half_vector halves = std::bit_cast<half_vector>(signed_bits);
+        const uint16_t packed = uint16_t(d4r_cvt_pk_fp8_f32(float(halves[0]), float(halves[1]), 0, false));
         return std::bit_cast<Fp8x2>(packed);
     }