diff --git a/hw/arm/smmuv3.c b/hw/arm/smmuv3.c
index 10c67645a5..c2946d8d23 100644
--- a/hw/arm/smmuv3.c
+++ b/hw/arm/smmuv3.c
@@ -1688,6 +1688,13 @@ static MemTxResult smmu_writel(SMMUv3State *s, hwaddr offset,
         s->strtab_base_cfg = data;
         if (FIELD_EX32(data, STRTAB_BASE_CFG, FMT) == 1) {
             s->sid_split = FIELD_EX32(data, STRTAB_BASE_CFG, SPLIT);
+            if (s->sid_split != 6 && s->sid_split != 8 && s->sid_split != 10) {
+                /* Other values are reserved, behave as 6 */
+                qemu_log_mask(LOG_GUEST_ERROR,
+                              "Invalid STRTAB_BASE_CFG.SPLIT=%u, use 6 instead\n",
+                              s->sid_split);
+                s->sid_split = 6;
+            }
             s->features |= SMMU_FEATURE_2LVL_STE;
         }
         break;