diff --git a/Python/ast.c b/Python/ast.c
index 7f379a5..c8875e0 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -692,7 +692,8 @@
     while (i < NCH(n)) {
         ch = CHILD(n, i);
         switch (TYPE(ch)) {
-            case fpdef:
+            case fpdef: {
+                int complex_args = 0, parenthesized = 0;
             handle_fpdef:
                 /* XXX Need to worry about checking if TYPE(CHILD(n, i+1)) is
                    anything other than EQUAL or a comma? */
@@ -707,6 +708,12 @@
                     found_default = 1;
                 }
                 else if (found_default) {
+                    /* def f((x)=4): pass should raise an error.
+                       def f((x, (y))): pass will just incur the tuple unpacking warning. */
+                    if (parenthesized && !complex_args) {
+                        ast_error(n, "parenthesized arg with default");
+                        goto error;
+                    }
                     ast_error(n, 
                              "non-default argument follows default argument");
                     goto error;
@@ -719,6 +726,7 @@
                         if (Py_Py3kWarningFlag && !ast_warn(c, ch,
                             "tuple parameter unpacking has been removed in 3.x"))
                             goto error;
+                        complex_args = 1;
                         asdl_seq_SET(args, k++, compiler_complex_args(c, ch));
                         if (!asdl_seq_GET(args, k-1))
                                 goto error;
@@ -726,6 +734,7 @@
                         /* def foo((x)): setup for checking NAME below. */
                         /* Loop because there can be many parens and tuple
                            unpacking mixed in. */
+                        parenthesized = 1;
                         ch = CHILD(ch, 0);
                         assert(TYPE(ch) == fpdef);
                         goto handle_fpdef;
@@ -747,7 +756,13 @@
                                          
                 }
                 i += 2; /* the name and the comma */
+                if (parenthesized && Py_Py3kWarningFlag &&
+                    !ast_warn(c, ch, "parenthesized argument names "
+                              "are invalid in 3.x"))
+                    goto error;
+
                 break;
+            }
             case STAR:
                 if (!forbidden_check(c, CHILD(n, i+1), STR(CHILD(n, i+1))))
                     goto error;