diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h
index ecc0183196..09bb0fd408 100644
--- a/include/qapi/visitor-impl.h
+++ b/include/qapi/visitor-impl.h
@@ -55,6 +55,8 @@ struct Visitor
     void (*type_int64)(Visitor *v, int64_t *obj, const char *name, Error **errp);
     /* visit_type_size() falls back to (*type_uint64)() if type_size is unset */
     void (*type_size)(Visitor *v, uint64_t *obj, const char *name, Error **errp);
+    bool (*start_union)(Visitor *v, bool data_present, Error **errp);
+    void (*end_union)(Visitor *v, bool data_present, Error **errp);
 };
 
 void input_type_enum(Visitor *v, int *obj, const char *strings[],
diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
index 4a0178fa46..5934f59ad8 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -58,5 +58,7 @@ void visit_type_size(Visitor *v, uint64_t *obj, const char *name, Error **errp);
 void visit_type_bool(Visitor *v, bool *obj, const char *name, Error **errp);
 void visit_type_str(Visitor *v, char **obj, const char *name, Error **errp);
 void visit_type_number(Visitor *v, double *obj, const char *name, Error **errp);
+bool visit_start_union(Visitor *v, bool data_present, Error **errp);
+void visit_end_union(Visitor *v, bool data_present, Error **errp);
 
 #endif
diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index 55f8d4068c..b66b93ae2b 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -58,6 +58,21 @@ void visit_end_list(Visitor *v, Error **errp)
     v->end_list(v, errp);
 }
 
+bool visit_start_union(Visitor *v, bool data_present, Error **errp)
+{
+    if (v->start_union) {
+        return v->start_union(v, data_present, errp);
+    }
+    return true;
+}
+
+void visit_end_union(Visitor *v, bool data_present, Error **errp)
+{
+    if (v->end_union) {
+        v->end_union(v, data_present, errp);
+    }
+}
+
 void visit_optional(Visitor *v, bool *present, const char *name,
                     Error **errp)
 {
diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index df9f7fb657..8f845a2b29 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -358,6 +358,9 @@ void visit_type_%(name)s(Visitor *m, %(name)s **obj, const char *name, Error **e
         if (err) {
             goto out_obj;
         }
+        if (!visit_start_union(m, !!(*obj)->data, &err) || err) {
+            goto out_obj;
+        }
         switch ((*obj)->kind) {
 ''',
                  disc_type = disc_type,
@@ -386,6 +389,9 @@ void visit_type_%(name)s(Visitor *m, %(name)s **obj, const char *name, Error **e
 out_obj:
         error_propagate(errp, err);
         err = NULL;
+        visit_end_union(m, !!(*obj)->data, &err);
+        error_propagate(errp, err);
+        err = NULL;
     }
     visit_end_struct(m, &err);
 out: