diff --git a/op_builder/builder.py b/op_builder/builder.py
index 465aa4399a90..ec7340410fc7 100644
--- a/op_builder/builder.py
+++ b/op_builder/builder.py
@@ -505,12 +505,14 @@ def simd_width(self):
             if cpu_info is None:
                 return '-D__SCALAR__'
 
+        # py-cpuinfo reports no 'flags' on some CPUs, e.g. Apple Silicon.
+        flags = cpu_info.get('flags', [])
         if cpu_info['arch'] == 'X86_64':
-            if 'avx512' in cpu_info['flags'] or 'avx512f' in cpu_info['flags']:
+            if 'avx512' in flags or 'avx512f' in flags:
                 return '-D__AVX512__'
-            elif 'avx2' in cpu_info['flags']:
+            elif 'avx2' in flags:
                 return '-D__AVX256__'
-        elif (cpu_info['arch'] or '').startswith('ARM') and 'sve' in cpu_info['flags']:
+        elif (cpu_info['arch'] or '').startswith('ARM') and 'sve' in flags:
             return '-D__SVE__'
         elif cpu_info['arch'] == 'ARM_8':
             # NEON is baseline on AArch64; vdivq/vsqrtq used by simd.h are A64-only,
diff --git a/tests/unit/ops/test_op_builder.py b/tests/unit/ops/test_op_builder.py
index 2bbfa0625f2d..941b2eb88195 100644
--- a/tests/unit/ops/test_op_builder.py
+++ b/tests/unit/ops/test_op_builder.py
@@ -338,3 +338,11 @@ def test_probe_is_compatible_does_not_propagate_a_failed_probe():
 @pytest.mark.parametrize("answer", [True, False])
 def test_probe_is_compatible_passes_through_a_successful_probe(answer):
     assert probe_is_compatible(_AnsweringBuilder(answer)) is answer
+
+
+@pytest.mark.parametrize("flags, expected", [(None, "-D__NEON__"), (["fp", "asimd", "sve"], "-D__SVE__")])
+def test_simd_width_handles_cpu_info_without_flags(flags, expected):
+    # py-cpuinfo leaves out 'flags' on Apple Silicon, so simd_width must not index it.
+    cpu_info = {"arch": "ARM_8"} if flags is None else {"arch": "ARM_8", "flags": flags}
+    with patch.dict(sys.modules, {"cpuinfo": MagicMock(get_cpu_info=MagicMock(return_value=cpu_info))}):
+        assert make_builder().simd_width() == expected