diff --git a/tools/widl/parser.y b/tools/widl/parser.y
index b8e1d4da50f..c9e8844c87c 100644
--- a/tools/widl/parser.y
+++ b/tools/widl/parser.y
@@ -1295,7 +1295,6 @@ type_t *make_type(unsigned char type, type_t *ref)
   t->attrs = NULL;
   t->orig = NULL;
   memset(&t->details, 0, sizeof(t->details));
-  t->ifaces = NULL;
   t->typestring_offset = 0;
   t->ptrdesc = 0;
   t->declarray = FALSE;
diff --git a/tools/widl/typetree.c b/tools/widl/typetree.c
index 8a42d565480..83650ee5dad 100644
--- a/tools/widl/typetree.c
+++ b/tools/widl/typetree.c
@@ -140,7 +140,7 @@ void type_module_define(type_t *module, statement_list_t *stmts)
 
 type_t *type_coclass_define(type_t *coclass, ifref_list_t *ifaces)
 {
-    coclass->ifaces = ifaces;
+    coclass->details.coclass.ifaces = ifaces;
     coclass->defined = TRUE;
     return coclass;
 }
diff --git a/tools/widl/typetree.h b/tools/widl/typetree.h
index af4d5e637e9..597531d74be 100644
--- a/tools/widl/typetree.h
+++ b/tools/widl/typetree.h
@@ -157,7 +157,7 @@ static inline int type_is_alias(const type_t *type)
 static inline ifref_list_t *type_coclass_get_ifaces(const type_t *type)
 {
     assert(type->type == RPC_FC_COCLASS);
-    return type->ifaces;
+    return type->details.coclass.ifaces;
 }
 
 #endif /* WIDL_TYPE_TREE_H */
diff --git a/tools/widl/widltypes.h b/tools/widl/widltypes.h
index 6835e626058..9dd23bf18a9 100644
--- a/tools/widl/widltypes.h
+++ b/tools/widl/widltypes.h
@@ -296,6 +296,11 @@ struct array_details
   expr_t *size_is, *length_is;
 };
 
+struct coclass_details
+{
+  ifref_list_t *ifaces;
+};
+
 struct _type_t {
   const char *name;
   unsigned char type;
@@ -309,8 +314,8 @@ struct _type_t {
     struct iface_details *iface;
     struct module_details *module;
     struct array_details array;
+    struct coclass_details coclass;
   } details;
-  ifref_list_t *ifaces;           /* coclasses */
   type_t *orig;                   /* dup'd types */
   unsigned int typestring_offset;
   unsigned int ptrdesc;           /* used for complex structs */