diff --git a/parso/python/normalizer.py b/parso/python/normalizer.py
index f4da332..d4c9710 100644
--- a/parso/python/normalizer.py
+++ b/parso/python/normalizer.py
@@ -33,6 +33,10 @@ def _is_future_import(import_from):
     return [n.value for n in from_names] == ['__future__']
 
 
+def _iter_params(parent_node):
+    return (n for n in parent_node.children if n.type == 'param')
+
+
 def _is_future_import_first(import_from):
     """
     Checks if the import is the first statement of a file.
@@ -173,6 +177,16 @@ class ErrorFinder(Normalizer):
                     if first_is_bytes != _is_bytes_literal(string):
                         self._add_syntax_error(message, node)
                         break
+        elif node.type in ('parameters', 'lambdef'):
+            default_only = False
+            for p in _iter_params(node):
+                if p.default is None:
+                    if default_only:
+                        # def f(x=3, y): pass
+                        message = "non-default argument follows default argument"
+                        self._add_syntax_error(message, node)
+                else:
+                    default_only = True
 
         yield
 
diff --git a/test/test_python_errors.py b/test/test_python_errors.py
index ef50e16..478deea 100644
--- a/test/test_python_errors.py
+++ b/test/test_python_errors.py
@@ -73,6 +73,12 @@ def test_indentation_errors(code, positions):
         'try: pass\nexcept: pass\nexcept X: pass',
         'f(x for x in bar, 1)',
         'from foo import a,',
+        'def f(x=3, y): pass',
+        'lambda x=3, y: x',
+        #'None = 1',
+        #'(True,) = x',
+        #'([False], a) = x',
+        #'__debug__ = 1'
 
         # IndentationError
         ' foo',
@@ -82,7 +88,6 @@ def test_indentation_errors(code, positions):
     ]
 )
 def test_python_exception_matches(code):
-    error, = _get_error_list(code)
     try:
         compile(code, '<unknown>', 'exec')
     except (SyntaxError, IndentationError) as e:
@@ -94,6 +99,8 @@ def test_python_exception_matches(code):
     # Python 2.6 has a bit different error messages here, so skip it.
     if sys.version_info[:2] == (2, 6) and wanted == 'SyntaxError: unexpected EOF while parsing':
         wanted = 'SyntaxError: invalid syntax'
+
+    error, = _get_error_list(code)
     assert wanted == error.message