http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58599
--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> --- Gah, sorry, you're right. In fact, started with r179156: $ ./cc1plus-179156 -quiet -std=c++0x ~/x.C /home/polacek/x.C: In substitution of ‘template<class, class ...> template<class> int A<0>::B::foo() [with <template-parameter-2-1> = <missing>, <template-parameter-1-1> = int, <template-parameter-1-2> = <missing>]’: /home/polacek/x.C:9:22: required from here /home/polacek/x.C:7:28: internal compiler error: tree check: accessed elt 2 of tree_vec with 1 elts in tsubst_pack_expansion, at cp/pt.c:9153 Please submit a full bug report, with preprocessed source if appropriate. See <http://gcc.gnu.org/bugs.html> for instructions.