diff --git a/target/s390x/misc_helper.c b/target/s390x/misc_helper.c
index 93b0e61366d12cbcd49171b2b675ad0cd6b29847..eca82441d05b60a869c78d52367ea28d93f58da0 100644
--- a/target/s390x/misc_helper.c
+++ b/target/s390x/misc_helper.c
@@ -288,7 +288,9 @@ void HELPER(diag)(CPUS390XState *env, uint32_t r1, uint32_t r3, uint32_t num)
     switch (num) {
     case 0x500:
         /* KVM hypercall */
+        qemu_mutex_lock_iothread();
         r = s390_virtio_hypercall(env);
+        qemu_mutex_unlock_iothread();
         break;
     case 0x44:
         /* yield */
@@ -515,7 +517,8 @@ uint32_t HELPER(sigp)(CPUS390XState *env, uint64_t order_code, uint32_t r1,
     /* Remember: Use "R1 or R1 + 1, whichever is the odd-numbered register"
        as parameter (input). Status (output) is always R1. */
 
-    switch (order_code) {
+    /* sigp contains the order code in bit positions 56-63, mask it here. */
+    switch (order_code & 0xff) {
     case SIGP_SET_ARCH:
         /* switch arch */
         break;