Index: src/os-openbsd.h
--- src/os-openbsd.h.orig
+++ src/os-openbsd.h
@@ -1,16 +1,34 @@
+#include <sys/cdefs.h>
+#include <sys/types.h>
+#include <sys/ioctl.h>
 #include <netinet/in_systm.h>
 #include <netinet/ip_mroute.h>
 #include <netinet/ip.h>
 #include <netinet/igmp.h>
 
+
+#ifndef IGMP_MEMBERSHIP_QUERY
 #define IGMP_MEMBERSHIP_QUERY IGMP_HOST_MEMBERSHIP_QUERY
+#endif
+#ifndef IGMP_V1_MEMBERSHIP_REPORT
 #define IGMP_V1_MEMBERSHIP_REPORT IGMP_v1_HOST_MEMBERSHIP_REPORT
+#endif
+#ifndef IGMP_V2_MEMBERSHIP_REPORT
 #define IGMP_V2_MEMBERSHIP_REPORT IGMP_v2_HOST_MEMBERSHIP_REPORT
+#endif
+#ifndef IGMP_V3_MEMBERSHIP_REPORT
 #define IGMP_V3_MEMBERSHIP_REPORT 0x22
+#endif
+#ifndef IGMP_V2_LEAVE_GROUP
 #define IGMP_V2_LEAVE_GROUP IGMP_HOST_LEAVE_MESSAGE
+#endif
 
+#ifndef INADDR_ALLRTRS_GROUP
 #define INADDR_ALLRTRS_GROUP INADDR_ALLROUTERS_GROUP
+#endif
+#ifndef INADDR_ALLIGMPV3_GROUP
 #define INADDR_ALLIGMPV3_GROUP ((in_addr_t) 0xe0000016)
+#endif
 
 static inline unsigned short ip_data_len(const struct ip *ip)
 {