Index: Python/ast.c
===================================================================
--- Python/ast.c	(revision 51856)
+++ Python/ast.c	(working copy)
@@ -637,6 +637,7 @@
 	ch = CHILD(n, i);
 	switch (TYPE(ch)) {
             case fpdef:
+            handle_fpdef:
                 /* XXX Need to worry about checking if TYPE(CHILD(n, i+1)) is
                    anything other than EQUAL or a comma? */
                 /* XXX Should NCH(n) check be made a separate check? */
@@ -662,7 +663,11 @@
 			asdl_seq_SET(args, k++, compiler_complex_args(c, ch));
 		    } else {
 			/* def foo((x)): setup for checking NAME below. */
+			/* Loop because there can be many parens and tuple
+			   unpacking mixed in. */
 			ch = CHILD(ch, 0);
+			assert(TYPE(ch) == fpdef);
+			goto handle_fpdef;
 		    }
                 }
                 if (TYPE(CHILD(ch, 0)) == NAME) {