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 */