diff --git a/configure b/configure
index 38ee257701..4d01a42ba6 100755
--- a/configure
+++ b/configure
@@ -512,10 +512,7 @@ case "$cpu" in
     cpu="x86_64"
     host_arch=x86_64
     linux_arch=x86
-    # ??? Only extremely old AMD cpus do not have cmpxchg16b.
-    # If we truly care, we should simply detect this case at
-    # runtime and generate the fallback to serial emulation.
-    CPU_CFLAGS="-m64 -mcx16"
+    CPU_CFLAGS="-m64"
     ;;
 esac
 
@@ -1203,7 +1200,7 @@ fi
 : ${cross_cc_cflags_sparc64="-m64 -mcpu=ultrasparc"}
 : ${cross_cc_sparc="$cross_cc_sparc64"}
 : ${cross_cc_cflags_sparc="-m32 -mcpu=supersparc"}
-: ${cross_cc_cflags_x86_64="-m64"}
+: ${cross_cc_cflags_x86_64="-m64 -mcx16"}
 
 compute_target_variable() {
   eval "$2="
diff --git a/meson.build b/meson.build
index a9de71d450..7fd82b5f48 100644
--- a/meson.build
+++ b/meson.build
@@ -336,6 +336,13 @@ if host_arch == 'i386' and not cc.links('''
   qemu_common_flags = ['-march=i486'] + qemu_common_flags
 endif
 
+# ??? Only extremely old AMD cpus do not have cmpxchg16b.
+# If we truly care, we should simply detect this case at
+# runtime and generate the fallback to serial emulation.
+if host_arch == 'x86_64'
+  qemu_common_flags = ['-mcx16'] + qemu_common_flags
+endif
+
 if get_option('prefer_static')
   qemu_ldflags += get_option('b_pie') ? '-static-pie' : '-static'
 endif