shishi's build log includes: configure: WARNING: no libresolv, SRV RRs not used checking for res_query in -lresolv... no and indeed, shishi fails to find kdcs using SRV records. This seems to be because libresolv exports __res_query, not res_query, and relies on macros in resolv.h to fix up the names. So, you're either going to need a more complex test using AC_LINK_IFELSE, or assume that if AC_CHECK_DECL says res_query is in resolv.h, then it will link when you use -lresolv