diff --git a/libguile/net_db.c b/libguile/net_db.c
index bcba18ebd..eb0c4c3eb 100644
--- a/libguile/net_db.c
+++ b/libguile/net_db.c
@@ -73,6 +73,17 @@ extern int h_errno;
 extern const char *hstrerror (int);
 #endif
 
+/* NetBSD 5.0 lacks the following flags.  */
+#ifndef AI_ALL
+# define AI_ALL 0
+#endif
+#ifndef AI_V4MAPPED
+# define AI_V4MAPPED 0
+#endif
+#ifndef AI_ADDRCONFIG
+# define AI_ADDRCONFIG 0
+#endif
+
 
 
 SCM_SYMBOL (scm_host_not_found_key, "host-not-found");