diff --git a/configure.in b/configure.in
index 54e0f175..52c28528 100644
--- a/configure.in
+++ b/configure.in
@@ -89,7 +89,12 @@ fi
 
 dnl Checks for header files.
 AC_HEADER_STDC
-AC_CHECK_HEADERS(fcntl.h stdarg.h inttypes.h stdint.h stddef.h poll.h unistd.h sys/epoll.h sys/time.h sys/queue.h sys/event.h sys/param.h sys/ioctl.h sys/select.h sys/devpoll.h port.h netinet/in.h netinet/in6.h sys/socket.h sys/uio.h arpa/inet.h sys/eventfd.h sys/mman.h sys/sendfile.h netdb.h sys/sysctl.h)
+AC_CHECK_HEADERS(fcntl.h stdarg.h inttypes.h stdint.h stddef.h poll.h unistd.h sys/epoll.h sys/time.h sys/queue.h sys/event.h sys/param.h sys/ioctl.h sys/select.h sys/devpoll.h port.h netinet/in.h netinet/in6.h sys/socket.h sys/uio.h arpa/inet.h sys/eventfd.h sys/mman.h sys/sendfile.h netdb.h)
+AC_CHECK_HEADERS(sys/sysctl.h, [], [], [
+#ifdef HAVE_SYS_PARAM_H
+#include <sys/param.h>
+#endif
+])
 if test "x$ac_cv_header_sys_queue_h" = "xyes"; then
 	AC_MSG_CHECKING(for TAILQ_FOREACH in sys/queue.h)
 	AC_EGREP_CPP(yes,
diff --git a/include/event2/util.h b/include/event2/util.h
index fd9a520a..13db8a63 100644
--- a/include/event2/util.h
+++ b/include/event2/util.h
@@ -137,6 +137,11 @@ extern "C" {
 #define ev_int8_t signed char
 #endif
 
+/* Some openbsd autoconf versions get the name of this macro wrong. */
+#if defined(_EVENT_SIZEOF_VOID__) && !defined(_EVENT_SIZEOF_VOID_P)
+#define _EVENT_SIZEOF_VOID_P _EVENT_SIZEOF_VOID__
+#endif
+
 #ifdef _EVENT_HAVE_UINTPTR_T
 #define ev_uintptr_t uintptr_t
 #define ev_intptr_t intptr_t