diff --git a/src/sim/core.c b/src/sim/core.c
index 63b3000..b93633c 100644
--- a/src/sim/core.c
+++ b/src/sim/core.c
@@ -300,8 +300,7 @@
 
 char *osim_print_sw(const struct osim_card_hdl *ch, uint16_t sw_in)
 {
-	/* FIXME: do we want to mark this as __thread? */
-	static char sw_print_buf[256];
+	static __thread char sw_print_buf[256];
 	return osim_print_sw_buf(sw_print_buf, sizeof(sw_print_buf), ch, sw_in);
 }