diff --git a/src/xbc/__init__.py b/src/xbc/__init__.py
index e26df55..b9a1109 100644
--- a/src/xbc/__init__.py
+++ b/src/xbc/__init__.py
@@ -215,12 +215,16 @@ def parse_block(key, seq):
                 if op == '+=':
                     if isinstance(ret[k], str):
                         assign = [ret[k]]
+                    elif ret[k] is True:
+                        assign = []
                     else:
                         assign = ret[k]
                     if isinstance(value, str):
                         assign.append(value)
                     else:
                         assign.extend(value)
+                    if isinstance(assign, list) and len(assign) == 1:
+                        assign = assign[0]
                 else:
                     assign = value
 
diff --git a/tests/test_bare.py b/tests/test_bare.py
index 3923c67..2e6ceba 100644
--- a/tests/test_bare.py
+++ b/tests/test_bare.py
@@ -65,3 +65,23 @@ def test_ovewrite_nonexistent():
     'Keys can only be updated if they exist.'
     with pytest.raises(ParseError):
         loads_xbc('a := 1')
+
+def test_append_key():
+    'Append an item to a key.'
+    assert loads_xbc('a; a += 1') == {'a': '1'}
+
+def test_append_single():
+    'Append an item to a single-item value.'
+    assert loads_xbc('a = 1; a += 2') == {'a': ['1', '2']}
+
+def test_append_single2():
+    'Append multiple items to a single-item value.'
+    assert loads_xbc('a = 1; a += 2, 3') == {'a': ['1', '2', '3']}
+
+def test_append_multi():
+    'Append an item to an array value'
+    assert loads_xbc('a = 1, 2; a += 3') == {'a': ['1', '2', '3']}
+
+def test_append_multi2():
+    'Append multiple items to an array value.'
+    assert loads_xbc('a = 1, 2; a += 3, 4') == {'a': ['1', '2', '3', '4']}