diff --git a/parso/python/diff.py b/parso/python/diff.py
index bd181dc..8a05565 100644
--- a/parso/python/diff.py
+++ b/parso/python/diff.py
@@ -29,6 +29,16 @@ def _assert_valid_graph(node):
     except AttributeError:
         previous_leaf = node.get_previous_leaf()
 
+        # Ignore INDENT is necessary, because indent/dedent tokens don't
+        # contain value/prefix and are just around, because of the tokenizer.
+        if node.type == 'error_leaf' and node.token_type == 'INDENT':
+            return
+        while previous_leaf and previous_leaf.type == 'error_leaf' \
+                and previous_leaf.token_type == 'INDENT':
+            assert previous_leaf.end_pos <= node.start_pos, \
+                (previous_leaf, node)
+            previous_leaf = previous_leaf.get_previous_leaf()
+
         # Calculate the content between two start positions.
         if previous_leaf is None:
             content = node.prefix
diff --git a/test/test_diff_parser.py b/test/test_diff_parser.py
index 8df6402..dd5366f 100644
--- a/test/test_diff_parser.py
+++ b/test/test_diff_parser.py
@@ -59,11 +59,11 @@ class Differ(object):
         new_module = diff_parser.update(self.lines, lines)
         self.lines = lines
         assert code == new_module.get_code()
+        _assert_valid_graph(new_module)
         assert diff_parser._copy_count == copies
         assert diff_parser._parser_count == parsers
 
         assert expect_error_leaves == _check_error_leaves_nodes(new_module)
-        _assert_valid_graph(new_module)
         return new_module
 
 
@@ -573,3 +573,9 @@ def test_if_removal_and_reappearence(differ):
     differ.parse(code2, parsers=1, copies=4, expect_error_leaves=True)
     differ.parse(code1, parsers=1, copies=1)
     differ.parse(code3, parsers=1, copies=1)
+
+
+def test_add_error_indentation(differ):
+    code = 'if x:\n 1\n'
+    differ.initialize(code)
+    differ.parse(code + '  2\n', parsers=1, copies=0, expect_error_leaves=True)