diff --git a/include/portable.h.in b/include/portable.h.in
index 2f653160a5..1175b99931 100644
--- a/include/portable.h.in
+++ b/include/portable.h.in
@@ -748,7 +748,9 @@
 #undef HAVE_CYRUS_SASL
 
 /* set to urandom device */
+#ifndef URANDOM_DEVICE
 #undef URANDOM_DEVICE
+#endif
 
 /* define if you actually have FreeBSD fetch(3) */
 #undef HAVE_FETCH