diff --git a/target-s390x/cpu.h b/target-s390x/cpu.h
index adb9a84237..584e74b89a 100644
--- a/target-s390x/cpu.h
+++ b/target-s390x/cpu.h
@@ -302,15 +302,20 @@ static inline CPU_DoubleU *get_freg(CPUS390XState *cs, int nr)
 #define CR0_LOWPROT             0x0000000010000000ULL
 #define CR0_EDAT                0x0000000000800000ULL
 
+/* MMU */
+#define MMU_PRIMARY_IDX         0
+#define MMU_SECONDARY_IDX       1
+#define MMU_HOME_IDX            2
+
 static inline int cpu_mmu_index (CPUS390XState *env)
 {
     switch (env->psw.mask & PSW_MASK_ASC) {
     case PSW_ASC_PRIMARY:
-        return 0;
+        return MMU_PRIMARY_IDX;
     case PSW_ASC_SECONDARY:
-        return 1;
+        return MMU_SECONDARY_IDX;
     case PSW_ASC_HOME:
-        return 2;
+        return MMU_HOME_IDX;
     case PSW_ASC_ACCREG:
         /* Fallthrough: access register mode is not yet supported */
     default:
@@ -318,6 +323,20 @@ static inline int cpu_mmu_index (CPUS390XState *env)
     }
 }
 
+static inline uint64_t cpu_mmu_idx_to_asc(int mmu_idx)
+{
+    switch (mmu_idx) {
+    case MMU_PRIMARY_IDX:
+        return PSW_ASC_PRIMARY;
+    case MMU_SECONDARY_IDX:
+        return PSW_ASC_SECONDARY;
+    case MMU_HOME_IDX:
+        return PSW_ASC_HOME;
+    default:
+        abort();
+    }
+}
+
 static inline void cpu_get_tb_cpu_state(CPUS390XState* env, target_ulong *pc,
                                         target_ulong *cs_base, int *flags)
 {