--- coregrind/m_syswrap/syswrap-x86-openbsd.c.orig
+++ coregrind/m_syswrap/syswrap-x86-openbsd.c
@@ -525,6 +525,15 @@
 #define PRE(name)       DEFN_PRE_TEMPLATE(openbsd, name)
 #define POST(name)      DEFN_POST_TEMPLATE(openbsd, name)
 
+PRE(sys___tfork_thread)
+{
+// XXXTBD
+}
+POST(sys___tfork_thread)
+{
+// XXXTBD
+}
+
 #if 0
 struct thr_param {
     void        (*start_func)(void *);  /* thread entry function. */
