--- openbsd-compat/explicit_bzero.c.orig
+++ openbsd-compat/explicit_bzero.c
@@ -10,6 +10,8 @@
 #if !defined(HAVE_EXPLICIT_BZERO) && !defined(_WIN32)

 #include <string.h>
+/* declare bzero explicitly: hidden by _POSIX_C_SOURCE on older SDKs */
+extern void bzero(void *, size_t);

 /*
  * explicit_bzero - don't let the compiler optimize away bzero