Index: Python/ast.c
===================================================================
--- Python/ast.c	(revision 81991)
+++ Python/ast.c	(working copy)
@@ -1749,13 +1749,22 @@
         TYPE((patom = CHILD(ppower, 0))) == atom &&
         TYPE((pnum = CHILD(patom, 0))) == NUMBER) {
         char *s = PyObject_MALLOC(strlen(STR(pnum)) + 2);
+        char *str_pnum_orig;
+        expr_ty result;
         if (s == NULL)
             return NULL;
         s[0] = '-';
+        /* Replace STR(pnum) with a negated string.  This (temporarily) leaves
+           the CST incorrect, so we restore the old value of STR(pnum) after
+           converting pnum to AST.  See issue #9011.
+        */
         strcpy(s + 1, STR(pnum));
-        PyObject_FREE(STR(pnum));
+        str_pnum_orig = STR(pnum);
         STR(pnum) = s;
-        return ast_for_atom(c, patom);
+        result = ast_for_atom(c, patom);
+        STR(pnum) = str_pnum_orig;
+        PyObject_FREE(s);
+        return result;
     }
 
     expression = ast_for_expr(c, CHILD(n, 1));
Index: Lib/test/test_parser.py
===================================================================
--- Lib/test/test_parser.py	(revision 81991)
+++ Lib/test/test_parser.py	(working copy)
@@ -532,8 +532,18 @@
         st = parser.suite('a = u"\u1"')
         self.assertRaises(SyntaxError, parser.compilest, st)
 
+    def test_issue_9011(self):
+        # Issue 9011: compilation of an unary minus expression changed
+        # the meaning of the ST, so that a second compilation produced
+        # incorrect results.
+        st = parser.expr('-3')
+        code1 = parser.compilest(st)
+        self.assertEqual(eval(code1), -3)
+        code2 = parser.compilest(st)
+        self.assertEqual(eval(code2), -3)
+
 class ParserStackLimitTestCase(unittest.TestCase):
-    """try to push the parser to/over it's limits.
+    """try to push the parser to/over its limits.
     see http://bugs.python.org/issue1881 for a discussion
     """
     def _nested_expression(self, level):