diff --git a/src/c/_cffi_backend.c b/src/c/_cffi_backend.c
index 20e964ba..0482bb67 100644
--- a/src/c/_cffi_backend.c
+++ b/src/c/_cffi_backend.c
@@ -630,16 +630,10 @@ get_field_name(CTypeDescrObject *ct, CFieldObject *cf);   /* forward */
 static int do_realize_lazy_struct(CTypeDescrObject *ct);
 /* forward, implemented in realize_c_type.c */
 
-static int ct_is_hidden(CTypeDescrObject *ct)
-{
-  return ((ct->ct_flags & CT_IS_OPAQUE) ||
-          (ct->ct_flags_mut & CT_UNDER_CONSTRUCTION));
-}
-
 static PyObject *ctypeget_fields(CTypeDescrObject *ct, void *context)
 {
     if (ct->ct_flags & (CT_STRUCT | CT_UNION)) {
-        if (!ct_is_hidden(ct)) {
+        if (!(ct->ct_flags & CT_IS_OPAQUE)) {
             CFieldObject *cf;
             PyObject *res;
             if (force_lazy_struct(ct) < 0)
@@ -1950,7 +1944,7 @@ get_alignment(CTypeDescrObject *ct)
     int align;
  retry:
     if ((ct->ct_flags & (CT_PRIMITIVE_ANY|CT_STRUCT|CT_UNION)) &&
-        !ct_is_hidden(ct)) {
+        !(ct->ct_flags & CT_IS_OPAQUE)) {
         align = ct->ct_length;
         if (align == -1 && (ct->ct_flags_mut & CT_LAZY_FIELD_LIST)) {
             force_lazy_struct(ct);
@@ -3347,9 +3341,8 @@ static PyObject *cdata_dir(PyObject *cd, PyObject *noarg)
     if (ct->ct_flags & CT_POINTER) {
         ct = ct->ct_itemdescr;
     }
-    // NJG: not sure this does the right thing if a type is already under construction
     if ((ct->ct_flags & (CT_STRUCT | CT_UNION)) &&
-        !ct_is_hidden(ct)) {
+        !(ct->ct_flags & CT_IS_OPAQUE)) {
 
         /* for non-opaque structs or unions */
         if (force_lazy_struct(ct) < 0)
@@ -5319,11 +5312,12 @@ static PyObject *b_complete_struct_or_union(PyObject *self, PyObject *args)
 
     is_union = ct->ct_flags & CT_UNION;
     if (!((ct->ct_flags & CT_UNION) || (ct->ct_flags & CT_STRUCT)) ||
-        !ct_is_hidden(ct)) {
+        !((ct->ct_flags & CT_IS_OPAQUE) || (ct->ct_flags_mut & CT_UNDER_CONSTRUCTION))) {
         PyErr_SetString(PyExc_TypeError,
                         "first arg must be a non-initialized struct or union ctype");
         return NULL;
     }
+    assert((ct->ct_flags & CT_IS_OPAQUE) ^ (ct->ct_flags_mut & CT_UNDER_CONSTRUCTION));
     ct->ct_flags_mut &= ~(CT_CUSTOM_FIELD_POS | CT_WITH_PACKED_CHANGE);
 
     alignment = 1;
@@ -5352,7 +5346,7 @@ static PyObject *b_complete_struct_or_union(PyObject *self, PyObject *args)
             goto error;
 
         if ((ftype->ct_flags & (CT_STRUCT | CT_UNION)) &&
-            !ct_is_hidden(ftype)) {
+            !(ftype->ct_flags & CT_IS_OPAQUE)) {
             /* force now the type of the nested field */
             if (force_lazy_struct(ftype) < 0)
                 return NULL;
diff --git a/src/c/realize_c_type.c b/src/c/realize_c_type.c
index 04cafb92..4677cf4b 100644
--- a/src/c/realize_c_type.c
+++ b/src/c/realize_c_type.c
@@ -778,7 +778,7 @@ static int do_realize_lazy_struct(CTypeDescrObject *ct)
 {
     /* This is called by force_lazy_struct() in _cffi_backend.c */
     assert(ct->ct_flags & (CT_STRUCT | CT_UNION));
-
+    assert(!(ct->ct_flags_mut & CT_UNDER_CONSTRUCTION));
     if (ct->ct_flags_mut & CT_LAZY_FIELD_LIST) {
         builder_c_t *builder;
         char *p;
@@ -787,8 +787,8 @@ static int do_realize_lazy_struct(CTypeDescrObject *ct)
         const struct _cffi_field_s *fld;
         PyObject *fields, *args, *res;
 
-        assert(!((ct->ct_flags & CT_IS_OPAQUE) ||
-                 (ct->ct_flags_mut & CT_UNDER_CONSTRUCTION)));
+        // opaque types should never set CT_LAZY_FIELD_LIST
+        assert(!(ct->ct_flags & CT_IS_OPAQUE));
 
         builder = ct->ct_extra;
         assert(builder != NULL);
@@ -884,11 +884,11 @@ static int do_realize_lazy_struct(CTypeDescrObject *ct)
 
         assert(ct->ct_stuff != NULL);
         ct->ct_flags_mut &= ~CT_LAZY_FIELD_LIST;
+        assert(!(ct->ct_flags_mut & CT_UNDER_CONSTRUCTION));
         Py_DECREF(res);
         return 1;
     }
     else {
-        assert(!(ct->ct_flags_mut & CT_UNDER_CONSTRUCTION));
         return 0;
     }
 }