diff --git a/lib/isc/lfsr.c b/lib/isc/lfsr.c
index ec4113b6de..10ea7d22dd 100644
--- a/lib/isc/lfsr.c
+++ b/lib/isc/lfsr.c
@@ -15,6 +15,8 @@
  * SOFTWARE.
  */
 
+#include <config.h>
+
 #include <stdlib.h>
 
 #include <isc/assertions.h>