diff --git a/jedi/parser/pgen2/parse.py b/jedi/parser/pgen2/parse.py
index 7a533890..5614081a 100644
--- a/jedi/parser/pgen2/parse.py
+++ b/jedi/parser/pgen2/parse.py
@@ -178,10 +178,15 @@ class Parser(object):
     def pop(self):
         """Pop a nonterminal.  (Internal)"""
         popdfa, popstate, popnode = self.stack.pop()
-        newnode = self.convert(self.grammar, popnode)
-        if newnode is not None:
-            if self.stack:
-                dfa, state, node = self.stack[-1]
-                node[-1].append(newnode)
-            else:
-                self.rootnode = newnode
+        children = popnode[3]
+        if len(children) != 1 or popnode[0] in (self.grammar.symbol2number['expr_stmt'],
+                                                self.grammar.symbol2number['file_input']):
+            newnode = self.convert(self.grammar, popnode)
+        else:
+            newnode = children[0]
+
+        if self.stack:
+            dfa, state, node = self.stack[-1]
+            node[-1].append(newnode)
+        else:
+            self.rootnode = newnode
diff --git a/jedi/parser/pytree.py b/jedi/parser/pytree.py
index dbb9a6b9..16fb6690 100644
--- a/jedi/parser/pytree.py
+++ b/jedi/parser/pytree.py
@@ -57,15 +57,7 @@ def type_repr(type_num):
     return _type_reprs.setdefault(type_num, type_num)
 
 
-def convert(grammar, raw_node):
-    """
-    Convert raw node information to a Node or Leaf instance.
-
-    This is passed to the parser driver which calls it whenever a reduction of a
-    grammar rule produces a new complete node, so that the tree is build
-    strictly bottom-up.
-    """
-
+def gen_ast_mapping():
     from jedi.parser import representation as pr
     _ast_mapping = {
         'expr_stmt': pr.ExprStmt,
@@ -91,9 +83,23 @@ def convert(grammar, raw_node):
         'try_stmt': pr.TryStmt,
     }
 
+    global ast_mapping, pr
     ast_mapping = dict((getattr(python_symbols, k), v) for k, v in _ast_mapping.items())
 
 
+def convert(grammar, raw_node):
+    """
+    Convert raw node information to a Node or Leaf instance.
+
+    This is passed to the parser driver which calls it whenever a reduction of a
+    grammar rule produces a new complete node, so that the tree is build
+    strictly bottom-up.
+    """
+    try:
+        ast_mapping
+    except NameError:
+        gen_ast_mapping()
+
     #import pdb; pdb.set_trace()
     type, value, context, children = raw_node
     if type in grammar.number2symbol: