--- coregrind/m_libcsignal.c.orig
+++ coregrind/m_libcsignal.c
@@ -397,6 +397,7 @@
 Int VG_(tkill)( Int lwpid, Int signo )
 {
 #  if defined(__NR_tkill)
+   PRINT("sys___tfork ( %ld, %ld )",ARG1,ARG2);
    SysRes res = VG_(mk_SysRes_Error)(VKI_ENOSYS);
    res = VG_(do_syscall2)(__NR_tkill, lwpid, signo);
    if (sr_isError(res) && sr_Err(res) == VKI_ENOSYS)
@@ -415,7 +416,9 @@
    return sr_isError(res) ? -1 : 0;
 
 #  elif defined(VGO_openbsd)
-   I_die_here;
+   SysRes res;
+   res = VG_(do_syscall3)(__NR_thrkill, lwpid, signo, NULL);
+   return sr_isError(res) ? -1 : 0;
 
 #  else
 #    error "Unsupported plat"
