Bad interaction with c-ts-mode

[heraplem]

I have c-ts-mode set as the default mode for C files. It seems that this is causing problems with certain primitive functions. If I type M-x helpful-symbol RET memq, I get the following error:

Wrong type argument: stringp, ("\\(?:\\^class_specifier\\$\\|compound_statement\\|e\\(?:num_specifier\\|xpression_statement\\)\\|function_definition\\|namespace_definition\\|preproc_\\(?:\\(?:function_\\)?def\\)\\|struct_specifier\\|type_definition\\|union_specifier\\)" . c-ts-mode--defun-valid-p)

Note that this isn't all primitive functions: I can still query cons, for example.