diff --git a/selftest/config_test.ok b/selftest/config_test.ok
index 80b5a065..e1fb87dc 100644
--- a/selftest/config_test.ok
+++ b/selftest/config_test.ok
@@ -93,3 +93,20 @@ Validation: Error
 Validation: Error
 --- imsi[]: ERR: ValueError: Invalid IMSI: None
 Validation: Error
+- Combine dicts:
+- Combine dicts 2:
+- Combine lists:
+- Combine lists 2:
+- Combine lists 3:
+ValueError expected
+- Combine lists 4:
+ValueError expected
+- Combine lists 5:
+ValueError expected
+- Combine lists 6:
+- Combine lists 7:
+- Combine lists 8:
+- Combine lists 9:
+- Combine lists 10:
+- Combine lists 13:
+- Combine lists 14:
diff --git a/selftest/config_test.py b/selftest/config_test.py
index 61ec73aa..fa86adce 100755
--- a/selftest/config_test.py
+++ b/selftest/config_test.py
@@ -112,4 +112,105 @@ val(c)
 c['imsi'][2] = None
 val(c)
 
+print('- Combine dicts:')
+a = {'times': '2'}
+b = {'type': 'osmo-bts-trx'}
+res = {'times': '2', 'type': 'osmo-bts-trx'}
+config.combine(a, b)
+assert a == res
+
+print('- Combine dicts 2:')
+a = {'times': '1', 'label': 'foo', 'type': 'osmo-bts-trx'}
+b = {'type': 'osmo-bts-trx'}
+res = {'times': '1', 'label': 'foo', 'type': 'osmo-bts-trx'}
+config.combine(a, b)
+assert a == res
+
+print('- Combine lists:')
+a = { 'a_list': ['x', 'y', 'z'] }
+b = { 'a_list': ['y'] }
+res = {'a_list': ['x', 'y', 'z']}
+config.combine(a, b)
+assert a == res
+
+print('- Combine lists 2:')
+a = { 'a_list': ['x'] }
+b = { 'a_list': ['w', 'u', 'x', 'y', 'z'] }
+res = {'a_list': ['x', 'w', 'u', 'y', 'z']}
+config.combine(a, b)
+assert a == res
+
+print('- Combine lists 3:')
+a = { 'a_list': ['x', 3] }
+b = { 'a_list': ['y', 'z'] }
+try:
+    config.combine(a, b)
+except ValueError:
+    print("ValueError expected")
+
+print('- Combine lists 4:')
+a = { 'a_list': [2, 3] }
+b = { 'a_list': ['y', 'z'] }
+try:
+    config.combine(a, b)
+except ValueError:
+    print("ValueError expected")
+
+print('- Combine lists 5:')
+a = { 'a_list': [{}, {}] }
+b = { 'a_list': ['y', 'z'] }
+try:
+    config.combine(a, b)
+except ValueError:
+    print("ValueError expected")
+
+print('- Combine lists 6:')
+a = { 'a_list': [{}, {}] }
+b = { 'a_list': [{}] }
+res = {'a_list': [{}, {}]}
+config.combine(a, b)
+assert a == res
+
+print('- Combine lists 7:')
+a = { 'times': '1', 'label': 'foo', 'trx': [{'nominal power': '10'}, {'nominal power': '12'}] }
+b = { 'type': 'osmo-bts-trx', 'trx': [{'nominal power': '10'}, {'nominal power': '12'}] }
+res = {'times': '1', 'label': 'foo', 'trx': [{'nominal power': '10'}, {'nominal power': '12'}], 'type': 'osmo-bts-trx'}
+config.combine(a, b)
+assert a == res
+
+print('- Combine lists 8:')
+a = { 'times': '1', 'label': 'foo', 'trx': [{'nominal power': '10'}] }
+b = { 'type': 'osmo-bts-trx', 'trx': [{'nominal power': '10'}, {'nominal power': '12'}] }
+res = {'times': '1', 'label': 'foo', 'trx': [{'nominal power': '10'}, {'nominal power': '12'}], 'type': 'osmo-bts-trx'}
+config.combine(a, b)
+assert a == res
+
+print('- Combine lists 9:')
+a = { 'times': '1', 'label': 'foo', 'trx': [{'nominal power': '10'}, {'nominal power': '12'}] }
+b = { 'type': 'osmo-bts-trx', 'trx': [{'nominal power': '10'}] }
+res = {'times': '1', 'label': 'foo', 'trx': [{'nominal power': '10'}, {'nominal power': '12'}], 'type': 'osmo-bts-trx'}
+config.combine(a, b)
+assert a == res
+
+print('- Combine lists 10:')
+a = { 'times': '1', 'label': 'foo', 'trx': [{'nominal power': '10'}, {'nominal power': '12'}] }
+b = { 'type': 'osmo-bts-trx', 'trx': [{}, {'nominal power': '12'}] }
+res = {'times': '1', 'label': 'foo', 'trx': [{'nominal power': '10'}, {'nominal power': '12'}], 'type': 'osmo-bts-trx'}
+config.combine(a, b)
+assert a == res
+
+print('- Combine lists 13:')
+a = { 'times': '1', 'label': 'foo', 'trx': [{}, {'nominal power': '12'}] }
+b = { 'type': 'osmo-bts-trx', 'trx': [{'nominal power': '10'}, {'nominal power': '12'}] }
+res = {'times': '1', 'label': 'foo', 'trx': [{'nominal power': '10'}, {'nominal power': '12'}], 'type': 'osmo-bts-trx'}
+config.combine(a, b)
+assert a == res
+
+print('- Combine lists 14:')
+a = { 'times': '1', 'label': 'foo', 'trx': [] }
+b = { 'type': 'osmo-bts-trx', 'trx': [] }
+res = {'times': '1', 'label': 'foo', 'trx': [], 'type': 'osmo-bts-trx'}
+config.combine(a, b)
+assert a == res
+
 # vim: expandtab tabstop=4 shiftwidth=4
diff --git a/src/osmo_gsm_tester/config.py b/src/osmo_gsm_tester/config.py
index 27ce428b..0721c308 100644
--- a/src/osmo_gsm_tester/config.py
+++ b/src/osmo_gsm_tester/config.py
@@ -245,9 +245,23 @@ def combine(dest, src):
     if is_list(dest):
         if not is_list(src):
             raise ValueError('cannot combine list with a value of type: %r' % type(src))
-        for i in range(len(src)):
-            log.ctx(idx=i)
-            combine(dest[i], src[i])
+        # Validate that all elements in both lists are of the same type:
+        t = util.list_validate_same_elem_type(src + dest)
+        if t is None:
+            return # both lists are empty, return
+        # For lists of complex objects, we expect them to be sorted lists:
+        if t in (dict, list, tuple):
+            for i in range(len(dest)):
+                log.ctx(idx=i)
+                src_it = src[i] if i < len(src) else util.empty_instance_type(t)
+                combine(dest[i], src_it)
+            for i in range(len(dest), len(src)):
+                log.ctx(idx=i)
+                dest.append(src[i])
+        else: # for lists of basic elements, we handle them as unsorted sets:
+            for elem in src:
+                if elem not in dest:
+                    dest.append(elem)
         return
     if dest == src:
         return
diff --git a/src/osmo_gsm_tester/util.py b/src/osmo_gsm_tester/util.py
index 197dc97b..bb4c5245 100644
--- a/src/osmo_gsm_tester/util.py
+++ b/src/osmo_gsm_tester/util.py
@@ -314,4 +314,27 @@ def str2bool(val):
         return True
     raise ValueError('Invalid BOOL field: %r' % val)
 
+def list_validate_same_elem_type(li):
+    '''
+    Checks that all elements in the list are of the same type and returns that type.
+    If the list is empty, returns None
+    If one of the elements is not of the same type, it throws a ValueError exception.
+    '''
+    if len(li) == 0:
+        return None
+    t = type(li[0])
+    for elem in li:
+        if type(elem) != t:
+            raise ValueError('List contains elements of different types: %r vs %r' % (t, type(elem)))
+    return t
+
+def empty_instance_type(t):
+    if t == dict:
+        return {}
+    elif t == list:
+        return []
+    elif t == tuple:
+        return ()
+    raise ValueError('type %r not supported!' % t)
+
 # vim: expandtab tabstop=4 shiftwidth=4