diff --git a/jedi/parser/fast.py b/jedi/parser/fast.py
index 0a2e61d9..41f3a525 100644
--- a/jedi/parser/fast.py
+++ b/jedi/parser/fast.py
@@ -382,7 +382,7 @@ class FastParser(use_metaclass(CachedFastParser)):
                                                        line_offset, nodes)
                     last_end_line = self.current_node.parser.module.end_pos[0]
 
-                debug.dbg('While parsing %s, line %s slowed down the fast parser',
+                debug.dbg('While parsing %s, line %s slowed down the fast parser.',
                           self.module_path, line_offset)
 
             line_offset = next_line_offset
@@ -488,6 +488,16 @@ class FastTokenizer(object):
                 self._closed = True
             return current
 
+        if value in ('def', 'class') and self._parentheses_level \
+                and re.match('\n[ \t]*\Z', prefix):
+            # Account for the fact that an open parentheses before a function
+            # will reset the parentheses counter, but new lines before will
+            # still be ignored. So check the prefix.
+
+            # TODO what about flow parentheses counter resets in the tokenizer?
+            self._parentheses_level = 0
+            return self._close()
+
         # Parentheses ignore the indentation rules. The other three stand for
         # new lines.
         if self.previous[0] in (NEWLINE, INDENT, DEDENT) \
diff --git a/test/test_parser/test_fast_parser.py b/test/test_parser/test_fast_parser.py
index 88c1ad0d..7a524fab 100644
--- a/test/test_parser/test_fast_parser.py
+++ b/test/test_parser/test_fast_parser.py
@@ -333,7 +333,7 @@ def test_open_parentheses():
     cache.save_parser(None, None, p, pickling=False)
 
     # Now with a correct parser it should work perfectly well.
-    check_fp('isinstance()\n' + func, 1)
+    check_fp('isinstance()\n' + func, 1, 2)
 
 
 def test_strange_parentheses():