diff --git a/ast27/Python/ast.c b/ast27/Python/ast.c
index 9ae7d2b1..5340d332 100644
--- a/ast27/Python/ast.c
+++ b/ast27/Python/ast.c
@@ -3500,6 +3500,7 @@ parsenumber(struct compiling *c, const char *s)
         const char *end;
         long x;
         double dx;
+        int old_style_octal;
 #ifndef WITHOUT_COMPLEX
         Py_complex complex;
         int imflag;
@@ -3519,14 +3520,17 @@ parsenumber(struct compiling *c, const char *s)
                         return PyErr_NoMemory();
                 memcpy(copy, s, len);
                 copy[len - 1] = '\0';
-                PyObject *result = PyLong_FromString(copy, (char **)0, 0);
+                old_style_octal = len > 2 && copy[0] == '0' && copy[1] >= '0' && copy[1] <= '9';
+                PyObject *result = PyLong_FromString(copy, (char **)0, old_style_octal ? 8 : 0);
                 free(copy);
                 return result;
         }
         x = Ta27OS_strtol((char *)s, (char **)&end, 0);
         if (*end == '\0') {
-                if (errno != 0)
-                        return PyLong_FromString((char *)s, (char **)0, 0);
+                if (errno != 0) {
+                        old_style_octal = end - s > 1 && s[0] == '0' && s[1] >= '0' && s[1] <= '9';
+                        return PyLong_FromString((char *)s, (char **)0, old_style_octal ? 8 : 0);
+                }
                 return PyLong_FromLong(x);
         }
         /* XXX Huge floats may silently fail */