diff --git a/parso/python/diff.py b/parso/python/diff.py
index dfe311c..af9e492 100644
--- a/parso/python/diff.py
+++ b/parso/python/diff.py
@@ -23,6 +23,8 @@ DEBUG_DIFF_PARSER = False
 def _assert_valid_graph(node):
     """
     Checks if the parent/children relationship is correct.
+
+    This is a check that only runs during debugging/testing.
     """
     try:
         children = node.children
@@ -112,11 +114,15 @@ def _func_or_class_has_suite(node):
     return node.type in ('classdef', 'funcdef') and node.children[-1].type == 'suite'
 
 
-def suite_or_file_input_is_valid(pgen_grammar, stack):
+def _suite_or_file_input_is_valid(pgen_grammar, stack):
     if not _flows_finished(pgen_grammar, stack):
         return False
 
     for stack_node in reversed(stack):
+        if stack_node.nonterminal == 'decorator':
+            # A decorator is only valid with the upcoming function.
+            return False
+
         if stack_node.nonterminal == 'suite':
             # If only newline is in the suite, the suite is not valid, yet.
             return len(stack_node.nodes) > 1
@@ -388,7 +394,7 @@ class DiffParser(object):
             elif typ == PythonTokenTypes.NEWLINE and start_pos[0] >= until_line:
                 yield PythonToken(typ, string, start_pos, prefix)
                 # Check if the parser is actually in a valid suite state.
-                if suite_or_file_input_is_valid(self._pgen_grammar, stack):
+                if _suite_or_file_input_is_valid(self._pgen_grammar, stack):
                     start_pos = start_pos[0] + 1, 0
                     while len(indents) > int(omitted_first_indent):
                         indents.pop()
diff --git a/test/test_diff_parser.py b/test/test_diff_parser.py
index 46d51ef..530d967 100644
--- a/test/test_diff_parser.py
+++ b/test/test_diff_parser.py
@@ -59,6 +59,7 @@ 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
@@ -745,3 +746,42 @@ def test_paren_before_docstring(differ):
     differ.initialize(code1)
     differ.parse(code2, parsers=1, copies=1, expect_error_leaves=True)
     differ.parse(code1, parsers=2, copies=1)
+
+
+def test_x(differ):
+    code1 = dedent('''\
+        class StackNode(object):
+            def __init__(self, dfa):
+                self.dfa = dfa
+                self.nodes = []
+
+            @property
+            def nonterminal(self):
+                return self.dfa.from_rule
+
+            def __repr__(self):
+                return '%s(%s, %s)' % (self.__class__.__name__, self.dfa, self.nodes)
+
+        def x():
+            pass
+        ''')
+
+    code2 = dedent('''\
+        class StackNode(object):
+            def __init__(self, dfa):
+                self.dfa = dfa
+                self.nodes = []
+                           (msg, type_.name, value, start_pos))
+
+            @property
+            def nonterminal(self):
+
+            def __repr__(self):
+
+        def x():
+            pass
+        ''')
+
+    differ.initialize(code1)
+    differ.parse(code2, parsers=3, copies=1, expect_error_leaves=True)
+    differ.parse(code1, parsers=2, copies=2)