diff --git a/none/tests/s390x/stmg.c b/none/tests/s390x/stmg.c

index 21765f3..a1509c4 100644

--- a/none/tests/s390x/stmg.c

+++ b/none/tests/s390x/stmg.c

@@ -32,7 +32,7 @@ stmg_wrap(void)

                  "lg   15,  0(%1)\n\t"

                  "stmg 15, 2, %0\n\t"

                  "lgr  15, 3"          /* restore stack pointer */

-                 :"=S" (buf)

+                 :"=m" (buf)

                  : "a" (base)

                  : "0", "1", "2", "3");

    /* Write out BUF */