diff --git a/op_builder/cpu_adam.py b/op_builder/cpu_adam.py
index 20f8fe2d8b6f..054654d00c0f 100644
--- a/op_builder/cpu_adam.py
+++ b/op_builder/cpu_adam.py
@@ -36,7 +36,7 @@ def simd_width(self):
                 return '-D__AVX512__'
             elif 'avx2' in result:
                 return '-D__AVX256__'
-        return ''
+        return '-D__SCALAR__'
 
     def cxx_args(self):
         CUDA_LIB64 = os.path.join(torch.utils.cpp_extension.CUDA_HOME, "lib64")