diff --git a/cde/programs/dtcalc/ds_common.c b/cde/programs/dtcalc/ds_common.c
index 7a51d65f2..9b1ec6844 100644
--- a/cde/programs/dtcalc/ds_common.c
+++ b/cde/programs/dtcalc/ds_common.c
@@ -33,6 +33,7 @@
  */
 
 #include <stdio.h>
+#include <stdlib.h>
 #include "ds_common.h"
 
 #define  FREE    (void) free