diff --git a/hw/core/machine.c b/hw/core/machine.c
index b8d95eec32..0a23ae3106 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -1157,6 +1157,9 @@ static char *cpu_slot_to_string(const CPUArchId *cpu)
         g_string_append_printf(s, "socket-id: %"PRId64, cpu->props.socket_id);
     }
     if (cpu->props.has_die_id) {
+        if (s->len) {
+            g_string_append_printf(s, ", ");
+        }
         g_string_append_printf(s, "die-id: %"PRId64, cpu->props.die_id);
     }
     if (cpu->props.has_core_id) {