diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index b4f5094259..3206f379f8 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -1884,6 +1884,8 @@ static void vtd_context_device_invalidate(IntelIOMMUState *s,
     case 3:
         mask = 7;   /* Mask bit 2:0 in the SID field */
         break;
+    default:
+        g_assert_not_reached();
     }
     mask = ~mask;