diff --git a/src/kernel/build.h b/src/kernel/build.h
index 323003efd..39916365a 100644
--- a/src/kernel/build.h
+++ b/src/kernel/build.h
@@ -60,13 +60,7 @@ extern "C" {
         } extra;
 
         struct construction *improvement;
-        /* next level, if upgradable. if more than one of these items
-         * can be built (weapons, armour) per turn, must not be NULL,
-         * but point to the same type again:
-         *   const_sword.improvement = &const_sword
-         * last level of a building points to NULL, as do objects of
-         * an unlimited size.
-         */
+        /* next level, if upgradable. */
     } construction;
 
     void free_construction(struct construction *cons);
diff --git a/src/kernel/building.c b/src/kernel/building.c
index 9decc9039..bb97f57b8 100644
--- a/src/kernel/building.c
+++ b/src/kernel/building.c
@@ -192,7 +192,6 @@ const char *buildingtype(const building_type * btype, const building * b, int bs
     }
     if (btype->construction && btype->construction->extra.name) {
         if (b) {
-            assert(b->type == btype);
             bsize = adjust_size(b, bsize);
         }
         for (con = btype->construction; con; con = con->improvement) {
diff --git a/src/reports.c b/src/reports.c
index 353ed09fe..9af18c1d2 100644
--- a/src/reports.c
+++ b/src/reports.c
@@ -386,7 +386,7 @@ const char **illusion)
     if (illusion) {
         *illusion = NULL;
 
-        if (is_building_type(b->type, "illusioncastle")) {
+        if (b->attribs && is_building_type(b->type, "illusioncastle")) {
             const attrib *a = a_find(b->attribs, &at_icastle);
             if (a != NULL) {
                 *illusion = buildingtype(icastle_type(a), b, b->size);