diff --git a/src/bind_building.c b/src/bind_building.c
index 93576ed3b..d51122b0a 100644
--- a/src/bind_building.c
+++ b/src/bind_building.c
@@ -183,16 +183,20 @@ static int tolua_building_set_owner(lua_State * L)
 
 static int tolua_building_create(lua_State * L)
 {
-    region *r = (region *)tolua_tousertype(L, 1, 0);
-    const char *bname = tolua_tostring(L, 2, 0);
+    region *r = (region *)tolua_tousertype(L, 1, NULL);
+    const char *bname = tolua_tostring(L, 2, NULL);
+    int size = (int)tolua_tonumber(L, 3, 1);
     if (!r) {
         log_error("building.create expects a region as argument 1");
     } else if (!bname) {
         log_error("building.create expects a name as argument 2");
+    }
+    else if (size <= 0) {
+        log_error("building.create expects a size > 0");
     } else {
         const building_type *btype = bt_find(bname);
         if (btype) {
-            building *b = new_building(btype, r, default_locale);
+            building *b = new_building(btype, r, default_locale, size);
             tolua_pushusertype(L, (void *)b, TOLUA_CAST "building");
             return 1;
         }
diff --git a/src/kernel/build.c b/src/kernel/build.c
index 3eb9870de..76cbe9f34 100644
--- a/src/kernel/build.c
+++ b/src/kernel/build.c
@@ -827,8 +827,7 @@ build_building(unit * u, const building_type * btype, int id, int want, order *
         b->size += built;
     } else {
         /* build a new building */
-        b = new_building(btype, r, lang);
-        b->size = built;
+        b = new_building(btype, r, lang, built);
         b->type = btype;
         fset(b, BLD_MAINTAINED);
 
diff --git a/src/kernel/building.c b/src/kernel/building.c
index a6167f880..c8c19cc9d 100644
--- a/src/kernel/building.c
+++ b/src/kernel/building.c
@@ -369,7 +369,7 @@ building *building_create(int id)
 }
 
 building *new_building(const struct building_type * btype, region * r,
-    const struct locale * lang)
+    const struct locale * lang, int size)
 {
     building **bptr = &r->buildings;
     int id = newcontainerid();
@@ -377,6 +377,7 @@ building *new_building(const struct building_type * btype, region * r,
     const char *bname;
     char buffer[32];
 
+    assert(size > 0);
     b->type = btype;
     b->region = r;
     while (*bptr)
@@ -396,6 +397,7 @@ building *new_building(const struct building_type * btype, region * r,
     assert(bname);
     snprintf(buffer, sizeof(buffer), "%s %s", bname, itoa36(b->no));
     b->name = str_strdup(bname);
+    b->size = size;
     return b;
 }
 
diff --git a/src/kernel/building.h b/src/kernel/building.h
index 2471bbfdc..74128a036 100644
--- a/src/kernel/building.h
+++ b/src/kernel/building.h
@@ -111,7 +111,7 @@ extern "C" {
     int buildingcapacity(const struct building *b);
     struct building *building_create(int id);
     struct building *new_building(const struct building_type *typ,
-        struct region *r, const struct locale *lang);
+        struct region *r, const struct locale *lang, int size);
     int build_building(struct unit *u, const struct building_type *typ,
         int id, int size, struct order *ord);
     bool building_finished(const struct building *b);
diff --git a/src/laws.test.c b/src/laws.test.c
index 822f179e7..e830eb95f 100644
--- a/src/laws.test.c
+++ b/src/laws.test.c
@@ -61,7 +61,7 @@ static void test_rename_building(CuTest * tc)
     test_create_locale();
     btype = test_create_buildingtype("castle");
     r = test_create_region(0, 0, NULL);
-    b = new_building(btype, r, default_locale);
+    b = new_building(btype, r, default_locale, 1);
     f = test_create_faction(NULL);
     u = test_create_unit(f, r);
     u_set_building(u, b);
@@ -84,7 +84,7 @@ static void test_rename_building_twice(CuTest * tc)
     test_create_locale();
     btype = test_create_buildingtype("castle");
     r = test_create_region(0, 0, NULL);
-    b = new_building(btype, r, default_locale);
+    b = new_building(btype, r, default_locale, 1);
     f = test_create_faction(NULL);
     u = test_create_unit(f, r);
     u_set_building(u, b);
diff --git a/src/races/races.c b/src/races/races.c
index 7c3e65fc4..a782ba0ce 100644
--- a/src/races/races.c
+++ b/src/races/races.c
@@ -42,8 +42,7 @@ void equip_newunits(struct unit *u)
         if (u->building == NULL) {
             const building_type *btype = bt_find("castle");
             if (btype != NULL) {
-                building *b = new_building(btype, r, u->faction->locale);
-                b->size = 10;
+                building *b = new_building(btype, r, u->faction->locale, 10);
                 u_set_building(u, b);
                 building_set_owner(u);
             }
diff --git a/src/spells.c b/src/spells.c
index 518819cdd..fbd4d71d5 100644
--- a/src/spells.c
+++ b/src/spells.c
@@ -4415,7 +4415,7 @@ int sp_icastle(castorder * co)
     const building_type *type;
     region *r = co_get_region(co);
     unit *mage = co_get_caster(co);
-    int cast_level = co->level;
+    int size, cast_level = co->level;
     double power = co->force;
     spellparameter *pa = co->par;
     const char *bname;
@@ -4431,18 +4431,17 @@ int sp_icastle(castorder * co)
         type = bt_find("castle");
     }
 
-    b = new_building(bt_illusion, r, mage->faction->locale);
-
     /* Groesse festlegen. */
     if (type == bt_illusion) {
-        b->size = (rng_int() % (int)((power * power) + 1) * 10);
+        size = (rng_int() % (int)((power * power) + 1) * 10);
     }
     else if (type->maxsize > 0) {
-        b->size = type->maxsize;
+        size = type->maxsize;
     }
     else {
-        b->size = ((rng_int() % (int)(power)) + 1) * 5;
+        size = ((rng_int() % (int)(power)) + 1) * 5;
     }
+    b = new_building(bt_illusion, r, mage->faction->locale, size);
 
     bname = LOC(mage->faction->locale, buildingtype(type, b, 0));
     building_setname(b, bname);
diff --git a/src/tests.c b/src/tests.c
index 727803e2d..699c093d7 100644
--- a/src/tests.c
+++ b/src/tests.c
@@ -335,8 +335,7 @@ building * test_create_building(region * r, const building_type * btype)
         bt_castle->flags |= BTF_FORTIFICATION;
         btype = bt_castle;
     }
-    b = new_building(btype, r, default_locale);
-    b->size = btype->maxsize > 0 ? btype->maxsize : 1;
+    b = new_building(btype, r, default_locale, (btype->maxsize > 0) ? btype->maxsize : 1);
     return b;
 }
 
diff --git a/src/wormhole.c b/src/wormhole.c
index 22f2e3d8b..f4815f158 100644
--- a/src/wormhole.c
+++ b/src/wormhole.c
@@ -116,13 +116,13 @@ static attrib_type at_wormhole = {
 static void
 make_wormhole(const building_type * bt_wormhole, region * r1, region * r2)
 {
-    building *b1 = new_building(bt_wormhole, r1, default_locale);
-    building *b2 = new_building(bt_wormhole, r2, default_locale);
+    int size = bt_wormhole->maxcapacity * bt_wormhole->capacity;
+    building *b1 = new_building(bt_wormhole, r1, default_locale, size);
+    building *b2 = new_building(bt_wormhole, r2, default_locale, size);
     attrib *a1 = a_add(&b1->attribs, a_new(&at_wormhole));
     attrib *a2 = a_add(&b2->attribs, a_new(&at_wormhole));
     a1->data.v = b2->region;
     a2->data.v = b1->region;
-    b1->size = b2->size = bt_wormhole->maxcapacity * bt_wormhole->capacity;
     ADDMSG(&r1->msgs, msg_message("wormhole_appear", "region", r1));
     ADDMSG(&r2->msgs, msg_message("wormhole_appear", "region", r2));
 }