However, this doesn't happen when I start with emacs -Q. Here's the stack trace from the failure. It continues like this for thousands of repeating lines until aborting. I can help debug it under lldb, if you can tell me what to look for. John frame #203769: 0x0000000100166d5e Emacs`substitute_object_recurse + 302 frame #203770: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203771: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203772: 0x0000000100166d5e Emacs`substitute_object_recurse + 302 frame #203773: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203774: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203775: 0x0000000100166d5e Emacs`substitute_object_recurse + 302 frame #203776: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203777: 0x0000000100166d5e Emacs`substitute_object_recurse + 302 frame #203778: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203779: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203780: 0x0000000100166d5e Emacs`substitute_object_recurse + 302 frame #203781: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203782: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203783: 0x0000000100166d5e Emacs`substitute_object_recurse + 302 frame #203784: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203785: 0x0000000100166d5e Emacs`substitute_object_recurse + 302 frame #203786: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203787: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203788: 0x0000000100166d5e Emacs`substitute_object_recurse + 302 frame #203789: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203790: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203791: 0x0000000100166d5e Emacs`substitute_object_recurse + 302 frame #203792: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203793: 0x0000000100166d5e Emacs`substitute_object_recurse + 302 frame #203794: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203795: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203796: 0x0000000100166d5e Emacs`substitute_object_recurse + 302 frame #203797: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203798: 0x0000000100166d6e Emacs`substitute_object_recurse + 318 frame #203799: 0x0000000100166df4 Emacs`substitute_object_recurse + 452 frame #203800: 0x000000010016c3f5 Emacs`read1 + 7141 frame #203801: 0x000000010016a4fa Emacs`read_list + 90 frame #203802: 0x000000010016b5bf Emacs`read1 + 3503 frame #203803: 0x000000010016c059 Emacs`read1 + 6217 frame #203804: 0x000000010016a4fa Emacs`read_list + 90 frame #203805: 0x000000010016b5bf Emacs`read1 + 3503 frame #203806: 0x000000010016a4fa Emacs`read_list + 90 frame #203807: 0x000000010016b5bf Emacs`read1 + 3503 frame #203808: 0x000000010016a4fa Emacs`read_list + 90 frame #203809: 0x000000010016c998 Emacs`read_vector + 40 frame #203810: 0x000000010016b5ce Emacs`read1 + 3518 frame #203811: 0x000000010016a4fa Emacs`read_list + 90 frame #203812: 0x000000010016b5bf Emacs`read1 + 3503 frame #203813: 0x000000010016a4fa Emacs`read_list + 90 frame #203814: 0x000000010016c998 Emacs`read_vector + 40 frame #203815: 0x000000010016b5ce Emacs`read1 + 3518 frame #203816: 0x000000010016a4fa Emacs`read_list + 90 frame #203817: 0x000000010016b5bf Emacs`read1 + 3503 frame #203818: 0x000000010016a4fa Emacs`read_list + 90 frame #203819: 0x000000010016c998 Emacs`read_vector + 40 frame #203820: 0x000000010016b5ce Emacs`read1 + 3518 frame #203821: 0x000000010016a4fa Emacs`read_list + 90 frame #203822: 0x000000010016bb07 Emacs`read1 + 4855 frame #203823: 0x0000000100166a93 Emacs`read_internal_start + 483 frame #203824: 0x0000000100142471 Emacs`funcall_subr + 241 frame #203825: 0x0000000100141790 Emacs`Ffuncall + 832 frame #203826: 0x0000000100181220 Emacs`exec_byte_code + 1808 frame #203827: 0x0000000100141731 Emacs`Ffuncall + 737 frame #203828: 0x0000000100181220 Emacs`exec_byte_code + 1808 frame #203829: 0x0000000100141731 Emacs`Ffuncall + 737 frame #203830: 0x000000010014198f Emacs`Frun_hook_with_args + 255 frame #203831: 0x0000000100141814 Emacs`Frun_hooks + 68 frame #203832: 0x0000000100141790 Emacs`Ffuncall + 832 frame #203833: 0x0000000100181220 Emacs`exec_byte_code + 1808 frame #203834: 0x0000000100141731 Emacs`Ffuncall + 737 frame #203835: 0x0000000100181220 Emacs`exec_byte_code + 1808 frame #203836: 0x0000000100141731 Emacs`Ffuncall + 737 frame #203837: 0x0000000100181220 Emacs`exec_byte_code + 1808 frame #203838: 0x0000000100140eb4 Emacs`apply_lambda + 388 frame #203839: 0x000000010013d0cb Emacs`eval_sub + 923 frame #203840: 0x0000000100140e5e Emacs`apply_lambda + 302 frame #203841: 0x000000010013d0cb Emacs`eval_sub + 923 frame #203842: 0x000000010013d7ed Emacs`Fprogn + 45 frame #203843: 0x000000010013d284 Emacs`eval_sub + 1364 frame #203844: 0x000000010013d284 Emacs`eval_sub + 1364 frame #203845: 0x000000010013d1c2 Emacs`eval_sub + 1170 frame #203846: 0x000000010013e45d Emacs`FletX + 541 frame #203847: 0x000000010013d284 Emacs`eval_sub + 1364 frame #203848: 0x000000010013d7ed Emacs`Fprogn + 45 frame #203849: 0x000000010013d284 Emacs`eval_sub + 1364 frame #203850: 0x000000010013f6aa Emacs`Funwind_protect + 298 frame #203851: 0x000000010013d284 Emacs`eval_sub + 1364 frame #203852: 0x000000010013ea9d Emacs`Flet + 1021 frame #203853: 0x000000010013d284 Emacs`eval_sub + 1364 frame #203854: 0x000000010014291d Emacs`funcall_lambda + 893 frame #203855: 0x0000000100141731 Emacs`Ffuncall + 737 frame #203856: 0x000000010013a796 Emacs`Ffuncall_interactively + 70 frame #203857: 0x0000000100141790 Emacs`Ffuncall + 832 frame #203858: 0x000000010013acd0 Emacs`Fcall_interactively + 1312 frame #203859: 0x0000000100142495 Emacs`funcall_subr + 277 frame #203860: 0x0000000100141790 Emacs`Ffuncall + 832 frame #203861: 0x0000000100181220 Emacs`exec_byte_code + 1808 frame #203862: 0x0000000100141731 Emacs`Ffuncall + 737 frame #203863: 0x000000010014208c Emacs`call1 + 44 frame #203864: 0x00000001000bf21a Emacs`command_loop_1 + 1898 frame #203865: 0x000000010013fd63 Emacs`internal_condition_case + 259 frame #203866: 0x00000001000ce7a0 Emacs`command_loop_2 + 48 frame #203867: 0x000000010013f377 Emacs`internal_catch + 263 frame #203868: 0x00000001000bdf0e Emacs`command_loop + 158 frame #203869: 0x00000001000bde1f Emacs`recursive_edit_1 + 111 frame #203870: 0x00000001000be106 Emacs`Frecursive_edit + 406 frame #203871: 0x00000001000bcb02 Emacs`main + 6386 frame #203872: 0x00007fffb12b7235 libdyld.dylib`start + 1 In GNU Emacs 26.0.90 (build 2, x86_64-apple-darwin16.7.0, NS appkit-1504.83 Version 10.12.6 (Build 16G1036)) of 2017-11-20 built on Vulcan.local Repository revision: 617c55681307c2d8203778c9f654f279c7bddb27 Windowing system distributor 'Apple', version 10.3.1504 Recent messages: Loading message-x...done Loading /Users/johnw/.emacs.d/gnus-settings.el (source)...done Loading message-x...done Opening connection to Local via shell... Opening connection to Local...done nnimap read 0k from Local Saving file /Users/johnw/Messages/Gnus/.newsrc.eld... Wrote /Users/johnw/Messages/Gnus/.newsrc.eld Starting Fetchmail...done Starting Fetchmail...done Configured using: 'configure --prefix=/nix/store/2lf7r5cmykaagn4ri1lbv1cdchlk7yzh-emacs26 --with-ns --disable-ns-self-contained' Configured features: NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS Memory information: ((conses 16 726849 25911) (symbols 48 55309 2) (miscs 40 107 444) (strings 32 139729 12574) (string-bytes 1 4269703) (vectors 16 78409) (vector-slots 8 1188326 87634) (floats 8 631 352) (intervals 56 421 0) (buffers 992 22)) -- John Wiegley GPG fingerprint = 4710 CF98 AF9B 327B B80F http://newartisans.com 60E1 46C4 BD1A 7AC1 4BA2