diff --git a/lib/roken/warnerr.c b/lib/roken/warnerr.c
index b0e23b1b9..057fc23c7 100644
--- a/lib/roken/warnerr.c
+++ b/lib/roken/warnerr.c
@@ -47,6 +47,19 @@ RCSID("$Id$");
 const char *__progname;
 #endif
 
+void
+set_progname(char *argv0)
+{
+#ifndef HAVE___PROGNAME
+    char *p = strrchr(argv0, '/');
+    if(p == NULL)
+	p = argv0;
+    else
+	p++;
+    __progname = p;
+#endif
+}
+
 void
 warnerr(int doexit, int eval, int doerrno, const char *fmt, va_list ap)
 {