diff --git a/include/hw/s390x/event-facility.h b/include/hw/s390x/event-facility.h
index 6a062b668a..871f3e7f11 100644
--- a/include/hw/s390x/event-facility.h
+++ b/include/hw/s390x/event-facility.h
@@ -146,8 +146,10 @@ typedef struct WriteEventData {
 
 typedef struct ReadEventData {
     SCCBHeader h;
-    EventBufferHeader ebh;
-    uint32_t mask;
+    union {
+        uint32_t mask;
+        EventBufferHeader ebh;
+    };
 } QEMU_PACKED ReadEventData;
 
 typedef struct SCLPEvent {