diff --git a/lib/roken/unvis.c b/lib/roken/unvis.c
index db9a13caa..3142bb3da 100644
--- a/lib/roken/unvis.c
+++ b/lib/roken/unvis.c
@@ -39,6 +39,9 @@
 RCSID("$Id$");
 #endif
 #include <roken.h>
+#ifndef _DIAGASSERT
+#define _DIAGASSERT(X)
+#endif
 #else
 #include <sys/cdefs.h>
 #if defined(LIBC_SCCS) && !defined(lint)
diff --git a/lib/roken/vis.c b/lib/roken/vis.c
index 7a2123058..1c6c6338f 100644
--- a/lib/roken/vis.c
+++ b/lib/roken/vis.c
@@ -41,6 +41,9 @@
 RCSID("$Id$");
 #endif
 #include <roken.h>
+#ifndef _DIAGASSERT
+#define _DIAGASSERT(X)
+#endif
 #else
 #include <sys/cdefs.h>
 #if !defined(lint)