diff --git a/lib/isc/hex.c b/lib/isc/hex.c
index 59d8369a4e..e8861bc332 100644
--- a/lib/isc/hex.c
+++ b/lib/isc/hex.c
@@ -15,10 +15,12 @@
  * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: hex.c,v 1.5 2000/11/19 20:58:58 bwelling Exp $ */
+/* $Id: hex.c,v 1.6 2000/11/19 22:10:03 bwelling Exp $ */
 
 #include <config.h>
 
+#include <ctype.h>
+
 #include <isc/buffer.h>
 #include <isc/hex.h>
 #include <isc/lex.h>