diff --git a/target/s390x/tcg/mem_helper.c b/target/s390x/tcg/mem_helper.c
index e0befd0f03..3c0820dd74 100644
--- a/target/s390x/tcg/mem_helper.c
+++ b/target/s390x/tcg/mem_helper.c
@@ -2210,7 +2210,7 @@ void HELPER(sske)(CPUS390XState *env, uint64_t r1, uint64_t r2)
         skeyclass = S390_SKEYS_GET_CLASS(ss);
     }
 
-    key = (uint8_t) r1;
+    key = r1 & 0xfe;
     skeyclass->set_skeys(ss, addr / TARGET_PAGE_SIZE, 1, &key);
    /*
     * As we can only flush by virtual address and not all the entries