diff --git a/src/economy.c b/src/economy.c
index ecbd27db0..ffb9b0211 100644
--- a/src/economy.c
+++ b/src/economy.c
@@ -1174,7 +1174,8 @@ attrib_type at_trades = {
     NO_READ
 };
 
-static bool trade_needs_castle(const region *r, const race *rc) {
+bool trade_needs_castle(const terrain_type *terrain, const race *rc)
+{
     static int rc_change, terrain_change;
     static const race *rc_insect;
     static const terrain_type *t_desert, *t_swamp;
@@ -1185,7 +1186,7 @@ static bool trade_needs_castle(const region *r, const race *rc) {
         t_swamp = newterrain(T_SWAMP);
         t_desert = newterrain(T_DESERT);
     }
-    return rc != rc_insect && (r->terrain == t_swamp || r->terrain == t_desert);
+    return rc != rc_insect && (terrain == t_swamp || terrain == t_desert);
 }
 
 static void buy(unit * u, econ_request ** buyorders, struct order *ord)
@@ -1221,7 +1222,7 @@ static void buy(unit * u, econ_request ** buyorders, struct order *ord)
 
     /* Entweder man ist Insekt in Sumpf/Wueste, oder es muss
      * einen Handelsposten in der Region geben: */
-    if (trade_needs_castle(r, u_race(u))) {
+    if (trade_needs_castle(r->terrain, u_race(u))) {
         building *b = NULL;
         if (r->buildings) {
             static int cache;
diff --git a/src/economy.h b/src/economy.h
index 94c0997c8..2eace8a2d 100644
--- a/src/economy.h
+++ b/src/economy.h
@@ -49,6 +49,7 @@ extern "C" {
     struct faction;
     struct order;
     struct message;
+    struct terrain_type;
     struct item_type;
     
     typedef struct econ_request {
@@ -85,6 +86,8 @@ extern "C" {
     void destroy(struct region *r);
     void produce(struct region *r);
     void auto_work(struct region *r);
+    
+    bool trade_needs_castle(const struct terrain_type *terrain, const struct race *rc);
 
     typedef enum income_t { IC_WORK, IC_ENTERTAIN, IC_TAX, IC_TRADE, IC_TRADETAX, IC_STEAL, IC_MAGIC, IC_LOOT } income_t;
     void add_income(struct unit * u, income_t type, int want, int qty);
diff --git a/src/economy.test.c b/src/economy.test.c
index f4fe84340..a66e3d2ff 100644
--- a/src/economy.test.c
+++ b/src/economy.test.c
@@ -233,10 +233,31 @@ static unit *setup_trade_unit(CuTest *tc, region *r, const struct race *rc) {
     return u;
 }
 
+static void test_trade_needs_castle(CuTest *tc) {
+    /* Handeln ist nur in Regionen mit Burgen möglich. */
+    race *rc;
+    region *r;
+    const terrain_type *t_swamp;
+
+    test_setup();
+    setup_production();
+    test_create_locale();
+    setup_terrains(tc);
+    init_terrains();
+    t_swamp = get_terrain("swamp");
+    r = setup_trade_region(tc, t_swamp);
+    rc = test_create_race(NULL);
+
+    CuAssertTrue(tc, trade_needs_castle(t_swamp, rc));
+    test_teardown();
+}
+
 static void test_trade_insect(CuTest *tc) {
     /* Insekten koennen in Wuesten und Suempfen auch ohne Burgen handeln. */
     unit *u;
     region *r;
+    race *rc;
+    const terrain_type *t_swamp;
     const item_type *it_luxury;
     const item_type *it_silver;
 
@@ -244,14 +265,17 @@ static void test_trade_insect(CuTest *tc) {
     setup_production();
     test_create_locale();
     setup_terrains(tc);
-    r = setup_trade_region(tc, get_terrain("swamp"));
     init_terrains();
+    t_swamp = get_terrain("swamp");
+    rc = test_create_race("insect");
 
+    r = setup_trade_region(tc, t_swamp);
     it_luxury = r_luxury(r);
+    CuAssertTrue(tc, !trade_needs_castle(t_swamp, rc));
     CuAssertPtrNotNull(tc, it_luxury);
     it_silver = get_resourcetype(R_SILVER)->itype;
 
-    u = setup_trade_unit(tc, r, test_create_race("insect"));
+    u = setup_trade_unit(tc, r, rc);
     unit_addorder(u, create_order(K_BUY, u->faction->locale, "1 %s",
         LOC(u->faction->locale, resourcename(it_luxury->rtype, 0))));
 
@@ -796,6 +820,7 @@ CuSuite *get_economy_suite(void)
     SUITE_ADD_TEST(suite, test_heroes_dont_recruit);
     SUITE_ADD_TEST(suite, test_tax_cmd);
     SUITE_ADD_TEST(suite, test_buy_cmd);
+    SUITE_ADD_TEST(suite, test_trade_needs_castle);
     SUITE_ADD_TEST(suite, test_trade_insect);
     SUITE_ADD_TEST(suite, test_maintain_buildings);
     SUITE_ADD_TEST(suite, test_recruit);
diff --git a/src/tests.c b/src/tests.c
index c0350a9de..6dbc84271 100644
--- a/src/tests.c
+++ b/src/tests.c
@@ -583,7 +583,7 @@ struct message * test_find_messagetype_ex(struct message_list *msgs, const char
             return ml->msg;
         }
     }
-    return 0;
+    return NULL;
 }
 
 struct message * test_find_messagetype(struct message_list *msgs, const char *name)
@@ -603,7 +603,7 @@ void test_clear_messages(faction *f) {
     if (f->msgs) {
         free_messagelist(f->msgs->begin);
         free(f->msgs);
-        f->msgs = 0;
+        f->msgs = NULL;
     }
 }