diff --git a/src/kernel/building.c b/src/kernel/building.c
index 60b588912..0056fba1e 100644
--- a/src/kernel/building.c
+++ b/src/kernel/building.c
@@ -83,15 +83,28 @@ const building_type *bt_find(const char *name)
     return bt_find_i(name);
 }
 
+static int bt_changes = 1;
+
+bool bt_changed(int *cache)
+{
+    assert(cache);
+    if (*cache != bt_changes) {
+        *cache = bt_changes;
+        return true;
+    }
+    return false;
+}
+
 void bt_register(building_type * type)
 {
     if (type->init) {
         type->init(type);
     }
     ql_push(&buildingtypes, (void *)type);
+    ++bt_changes;
 }
 
-void free_buildingtype(void *ptr) {
+static void free_buildingtype(void *ptr) {
     building_type *btype = (building_type *)ptr;
     free_construction(btype->construction);
     free(btype->maintenance);
@@ -103,6 +116,7 @@ void free_buildingtypes(void) {
     ql_foreach(buildingtypes, free_buildingtype);
     ql_free(buildingtypes);
     buildingtypes = 0;
+    ++bt_changes;
 }
 
 building_type *bt_get_or_create(const char *name)
diff --git a/src/kernel/building.h b/src/kernel/building.h
index 587197276..dad9ffdde 100644
--- a/src/kernel/building.h
+++ b/src/kernel/building.h
@@ -84,6 +84,7 @@ extern "C" {
     extern struct attrib_type at_building_action;
 
     building_type *bt_get_or_create(const char *name);
+    bool bt_changed(int *cache);
     const building_type *bt_find(const char *name);
     void free_buildingtypes(void);
     void register_buildings(void);
diff --git a/src/kernel/building.test.c b/src/kernel/building.test.c
index 2f6fa6e34..755e9319f 100644
--- a/src/kernel/building.test.c
+++ b/src/kernel/building.test.c
@@ -17,16 +17,20 @@
 static void test_register_building(CuTest * tc)
 {
     building_type *btype;
+    int cache = 0;
 
     test_cleanup();
 
     btype = (building_type *)calloc(sizeof(building_type), 1);
     btype->_name = _strdup("herp");
+    CuAssertIntEquals(tc, true, bt_changed(&cache));
+    CuAssertIntEquals(tc, false, bt_changed(&cache));
     bt_register(btype);
+    CuAssertIntEquals(tc, true, bt_changed(&cache));
 
     CuAssertPtrNotNull(tc, bt_find("herp"));
-    //    free(btype->_name);
-    //    free(btype);
+    free_buildingtypes();
+    CuAssertIntEquals(tc, true, bt_changed(&cache));
     test_cleanup();
 }