diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index d41595eaa1..7a82b63766 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -234,6 +234,13 @@ void visit_type_int64(Visitor *v, int64_t *obj, const char *name, Error **errp)
     }
 }
 
+void visit_type_size(Visitor *v, uint64_t *obj, const char *name, Error **errp)
+{
+    if (!error_is_set(errp)) {
+        (v->type_size ? v->type_size : v->type_uint64)(v, obj, name, errp);
+    }
+}
+
 void visit_type_bool(Visitor *v, bool *obj, const char *name, Error **errp)
 {
     if (!error_is_set(errp)) {
diff --git a/qapi/qapi-visit-core.h b/qapi/qapi-visit-core.h
index a19d70c104..60acedac77 100644
--- a/qapi/qapi-visit-core.h
+++ b/qapi/qapi-visit-core.h
@@ -60,6 +60,8 @@ struct Visitor
     void (*type_int16)(Visitor *v, int16_t *obj, const char *name, Error **errp);
     void (*type_int32)(Visitor *v, int32_t *obj, const char *name, Error **errp);
     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);
 };
 
 void visit_start_handle(Visitor *v, void **obj, const char *kind,
@@ -85,6 +87,7 @@ void visit_type_int8(Visitor *v, int8_t *obj, const char *name, Error **errp);
 void visit_type_int16(Visitor *v, int16_t *obj, const char *name, Error **errp);
 void visit_type_int32(Visitor *v, int32_t *obj, const char *name, Error **errp);
 void visit_type_int64(Visitor *v, int64_t *obj, const char *name, Error **errp);
+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);
diff --git a/scripts/qapi.py b/scripts/qapi.py
index 1292476a7d..8082af3fcd 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -163,6 +163,8 @@ def c_type(name):
           name == 'int64' or name == 'uint8' or name == 'uint16' or
           name == 'uint32' or name == 'uint64'):
         return name + '_t'
+    elif name == 'size':
+        return 'uint64_t'
     elif name == 'bool':
         return 'bool'
     elif name == 'number':