diff --git a/scripts/tests/e2/buildings.lua b/scripts/tests/e2/buildings.lua
index 4797643e1..07b774d9c 100644
--- a/scripts/tests/e2/buildings.lua
+++ b/scripts/tests/e2/buildings.lua
@@ -51,3 +51,23 @@ function test_build_castle_stages()
     process_orders()
     assert_equal(250, b.size)
 end
+
+function test_build_maxsize()
+    local r = region.create(0,0, "plain")
+    local f = faction.create("human")
+    local u = unit.create(f, r, 100)
+    local b = building.create(r, "harbour")
+    
+    b.size = 20
+    u:add_item("stone", 1000)
+    u:add_item("log", 1000)
+    u:add_item("money", 10000)
+
+    u:set_skill("building", 100)
+    u:clear_orders()
+    u:add_order("MACHE BURG " .. itoa36(b.id))
+    process_orders()
+    assert_equal(25, b.size) -- build no more than max
+    process_orders()
+    assert_equal(25, b.size) -- stop at max
+end
diff --git a/src/kernel/building.c b/src/kernel/building.c
index bcc914cca..14e4a3e07 100644
--- a/src/kernel/building.c
+++ b/src/kernel/building.c
@@ -310,6 +310,7 @@ static const int watch_bonus[3] = { 0, 1, 2 };
 
 int building_protection(const building_type * btype, int stage)
 {
+    assert(btype->flags & BTF_FORTIFICATION);
     if (btype->maxsize < 0) {
         return castle_bonus[MIN(stage, 5)];
     }