diff --git a/GNUmakefile b/GNUmakefile
index afe9318..a9a50fe 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -167,16 +167,17 @@ adcrush_SOURCES := src/tools/adcrush.c
 admin_SOURCES := src/tools/admin.c
 
 autotest_SOURCES := \
-		autotest/test_message.tcc \
+		autotest/test_eventqueue.tcc \
+		autotest/test_hub.tcc \
+		autotest/test_inf.tcc \
+		autotest/test_ipfilter.tcc \
 		autotest/test_list.tcc \
 		autotest/test_memory.tcc \
-		autotest/test_ipfilter.tcc \
-		autotest/test_inf.tcc \
-		autotest/test_hub.tcc \
+		autotest/test_message.tcc \
 		autotest/test_misc.tcc \
+		autotest/test_sid.tcc \
 		autotest/test_tiger.tcc \
-		autotest/test_usermanager.tcc \
-		autotest/test_eventqueue.tcc
+		autotest/test_usermanager.tcc
 
 autotest_OBJECTS = autotest.o
 
diff --git a/autotest/test_sid.tcc b/autotest/test_sid.tcc
new file mode 100644
index 0000000..6445456
--- /dev/null
+++ b/autotest/test_sid.tcc
@@ -0,0 +1,138 @@
+#include <uhub.h>
+
+static struct sid_pool* sid_pool = 0;
+
+struct dummy_user
+{
+	sid_t sid;
+};
+
+static struct dummy_user* last = 0;
+sid_t last_sid = 0;
+
+EXO_TEST(sid_create_pool, {
+	sid_pool = sid_pool_create(4);
+	return sid_pool != 0;
+});
+
+EXO_TEST(sid_check_0a, {
+	struct dummy_user* user = (struct dummy_user*) sid_lookup(sid_pool, 0);
+	return user == 0;
+});
+
+EXO_TEST(sid_check_0b, {
+	struct dummy_user* user = (struct dummy_user*) sid_lookup(sid_pool, 5);
+	return user == 0;
+});
+
+EXO_TEST(sid_alloc_1, {
+	struct dummy_user* user = hub_malloc_zero(sizeof(struct dummy_user));
+	user->sid = sid_alloc(sid_pool, (struct hub_user*) user);
+	last = user;
+	last_sid = user->sid;
+	return (user->sid > 0 && user->sid < 1048576);
+});
+
+EXO_TEST(sid_check_1a, {
+	struct dummy_user* user = (struct dummy_user*) sid_lookup(sid_pool, last_sid);
+	return last == user;
+});
+
+EXO_TEST(sid_check_1b, {
+	struct dummy_user* user = (struct dummy_user*) sid_lookup(sid_pool, last_sid+1);
+	return user == 0;
+});
+
+EXO_TEST(sid_alloc_2, {
+	struct dummy_user* user = hub_malloc_zero(sizeof(struct dummy_user));
+	user->sid = sid_alloc(sid_pool, (struct hub_user*) user);
+	last_sid = user->sid;
+	return (user->sid > 0 && user->sid < 1048576);
+});
+
+EXO_TEST(sid_check_2, {
+	struct dummy_user* user = (struct dummy_user*) sid_lookup(sid_pool, last_sid);
+	return last != user;
+});
+
+EXO_TEST(sid_alloc_3, {
+	struct dummy_user* user = hub_malloc_zero(sizeof(struct dummy_user));
+	user->sid = sid_alloc(sid_pool, (struct hub_user*) user);
+	last_sid = user->sid;
+	return (user->sid > 0 && user->sid < 1048576);
+});
+
+EXO_TEST(sid_check_3, {
+	struct dummy_user* user = (struct dummy_user*) sid_lookup(sid_pool, last_sid);
+	return last != user;
+});
+
+EXO_TEST(sid_alloc_4, {
+	struct dummy_user* user = hub_malloc_zero(sizeof(struct dummy_user));
+	user->sid = sid_alloc(sid_pool, (struct hub_user*) user);
+	last_sid = user->sid;
+	return (user->sid > 0 && user->sid < 1048576);
+});
+
+EXO_TEST(sid_check_4, {
+	struct dummy_user* user = (struct dummy_user*) sid_lookup(sid_pool, last_sid);
+	return last != user;
+});
+
+EXO_TEST(sid_alloc_5, {
+	struct dummy_user user;
+	sid_t sid;
+	sid = sid_alloc(sid_pool, (struct hub_user*) &user);
+	return sid == 0;
+});
+
+EXO_TEST(sid_check_6, {
+	struct dummy_user* user = (struct dummy_user*) sid_lookup(sid_pool, 0);
+	return user == 0;
+});
+
+
+EXO_TEST(sid_list_all_1, {
+	sid_t s;
+	size_t n = 0;
+	int ok = 1;
+	for (s = last->sid; s <= last_sid; s++)
+	{
+		struct dummy_user* user = (struct dummy_user*) sid_lookup(sid_pool, s);
+		if (s != (user ? user->sid : -1))
+		{
+			ok = 0;
+			break;
+		}
+		n++;
+	}
+	return ok && n == 4;
+});
+
+#define FREE_SID(N) \
+	struct dummy_user* user = (struct dummy_user*) sid_lookup(sid_pool, N); \
+	sid_free(sid_pool, N); \
+	hub_free(user); \
+	return sid_lookup(sid_pool, N) == NULL;
+
+EXO_TEST(sid_remove_1, {
+	FREE_SID(2);
+});
+
+EXO_TEST(sid_remove_2, {
+	FREE_SID(1);
+});
+
+EXO_TEST(sid_remove_3, {
+	FREE_SID(4);
+});
+
+EXO_TEST(sid_remove_4, {
+	FREE_SID(3);
+});
+
+EXO_TEST(sid_destroy_pool, {
+	sid_pool_destroy(sid_pool);
+	sid_pool = 0;
+	return sid_pool == 0;
+});
diff --git a/src/adc/sid.c b/src/adc/sid.c
index c41151b..5531bec 100644
--- a/src/adc/sid.c
+++ b/src/adc/sid.c
@@ -119,6 +119,14 @@ void sid_pool_destroy(struct sid_pool* pool)
 
 sid_t sid_alloc(struct sid_pool* pool, struct hub_user* user)
 {
+	if (pool->count >= (pool->max - pool->min))
+	{
+#ifdef DEBUG_SID
+		LOG_DUMP("SID_POOL:  alloc, sid pool is full.");
+#endif
+		return 0;
+	}
+
 	sid_t n = (++pool->count);
 	for (; (pool->map[n % pool->max]); n++) ;
 
@@ -140,7 +148,7 @@ void sid_free(struct sid_pool* pool, sid_t sid)
 
 struct hub_user* sid_lookup(struct sid_pool* pool, sid_t sid)
 {
-	if (!sid || (sid > pool->max))
+	if (!sid || (sid >= pool->max))
 		return 0;
 	return pool->map[sid];
 }