diff --git a/src/x86/ffi.c b/src/x86/ffi.c
index cad32e8a0..73f69e095 100644
--- a/src/x86/ffi.c
+++ b/src/x86/ffi.c
@@ -177,7 +177,7 @@ ffi_prep_cif_machdep(ffi_cif *cif)
       bytes = FFI_ALIGN (bytes, t->alignment);
       bytes += FFI_ALIGN (t->size, FFI_SIZEOF_ARG);
     }
-  cif->bytes = FFI_ALIGN (bytes, 16);
+  cif->bytes = FFI_ALIGN (bytes, FFI_SIZEOF_ARG);
 
   return FFI_OK;
 }
diff --git a/src/x86/ffiw64.c b/src/x86/ffiw64.c
index f78752522..da44a0907 100644
--- a/src/x86/ffiw64.c
+++ b/src/x86/ffiw64.c
@@ -101,7 +101,7 @@ EFI64(ffi_prep_cif_machdep)(ffi_cif *cif)
   n += (flags == FFI_TYPE_STRUCT);
   if (n < 4)
     n = 4;
-  cif->bytes = n * 8;
+  cif->bytes = n * FFI_SIZEOF_ARG;
 
   return FFI_OK;
 }