diff --git a/jedi/evaluate/__init__.py b/jedi/evaluate/__init__.py
index 512cbb89..948a1330 100644
--- a/jedi/evaluate/__init__.py
+++ b/jedi/evaluate/__init__.py
@@ -154,10 +154,10 @@ class Evaluator(object):
             c_node = ContextualizedName(context, seek_name)
             types = finder.check_tuple_assignments(self, c_node, types)
 
-        first_operation = stmt.first_operation()
-        if first_operation not in ('=', None) and first_operation.type == 'operator':
+        first_operator = next(stmt.yield_operators(), None)
+        if first_operator not in ('=', None) and first_operator.type == 'operator':
             # `=` is always the last character in aug assignments -> -1
-            operator = copy.copy(first_operation)
+            operator = copy.copy(first_operator)
             operator.value = operator.value[:-1]
             name = str(stmt.get_defined_names()[0])
             left = context.py__getattribute__(
diff --git a/jedi/evaluate/finder.py b/jedi/evaluate/finder.py
index a18e63e4..2be77fb9 100644
--- a/jedi/evaluate/finder.py
+++ b/jedi/evaluate/finder.py
@@ -312,7 +312,7 @@ def _check_flow_information(context, flow, search_name, pos):
         for name in names:
             ass = tree.search_ancestor(name, 'assert_stmt')
             if ass is not None:
-                result = _check_isinstance_type(context, ass.assertion(), search_name)
+                result = _check_isinstance_type(context, ass.assertion, search_name)
                 if result is not None:
                     return result
 
diff --git a/jedi/parser/python/tree.py b/jedi/parser/python/tree.py
index 01a50adf..e2fb4b7b 100644
--- a/jedi/parser/python/tree.py
+++ b/jedi/parser/python/tree.py
@@ -965,6 +965,7 @@ class KeywordStatement(PythonBaseNode):
 class AssertStmt(KeywordStatement):
     __slots__ = ()
 
+    @property
     def assertion(self):
         return self.children[1]
 
@@ -972,9 +973,6 @@ class AssertStmt(KeywordStatement):
 class GlobalStmt(KeywordStatement):
     __slots__ = ()
 
-    def get_defined_names(self):
-        return []
-
     def get_global_names(self):
         return self.children[1::2]
 
@@ -984,12 +982,9 @@ class ReturnStmt(KeywordStatement):
 
 
 class YieldExpr(PythonBaseNode):
+    type = 'yield_expr'
     __slots__ = ()
 
-    @property
-    def type(self):
-        return 'yield_expr'
-
 
 def _defined_names(current):
     """
@@ -1030,14 +1025,20 @@ class ExprStmt(PythonBaseNode, DocstringMixin):
         """Returns the right-hand-side of the equals."""
         return self.children[-1]
 
-    def first_operation(self):
+    def yield_operators(self):
         """
-        Returns `+=`, `=`, etc or None if there is no operation.
+        Returns a generator of `+=`, `=`, etc. or None if there is no operation.
         """
-        try:
-            return self.children[1]
-        except IndexError:
-            return None
+        first = self.children[1]
+        if first.type == 'annassign':
+            if len(first.children) <= 2:
+                return  # No operator is available, it's just PEP 484.
+
+            first = first.children[2]
+        yield first
+
+        for operator in self.children[3::2]:
+            yield operator
 
 
 class Param(PythonBaseNode):
@@ -1109,6 +1110,7 @@ class Param(PythonBaseNode):
         return search_ancestor(self, ('funcdef', 'lambda'))
 
     def get_description(self):
+        # TODO Remove?
         children = self.children
         if children[-1] == ',':
             children = children[:-1]