diff --git a/share/machdeps/machdep_x86_64.json b/share/machdeps/machdep_x86_64.json
index d90f095c7ef5a781e55302d9053e97613206c671..b3b357f58cf722384ffefa692ad3c6faf6a6ac1d 100644
--- a/share/machdeps/machdep_x86_64.json
+++ b/share/machdeps/machdep_x86_64.json
@@ -12,7 +12,7 @@
     "alignof_str": 1,
     "char_is_unsigned": false,
     "compiler": "generic",
-    "cpp_arch_flags": "-m64",
+    "cpp_arch_flags": [ "-m64" ],
     "has__builtin_va_list": true,
     "little_endian": true,
     "ptrdiff_t": "long",