diff --git a/programs/pkey/dh_genprime.c b/programs/pkey/dh_genprime.c
index 072fe138f..84a94a18b 100644
--- a/programs/pkey/dh_genprime.c
+++ b/programs/pkey/dh_genprime.c
@@ -29,6 +29,7 @@
 #include "mbedtls/platform.h"
 #else
 #include <stdio.h>
+#include <stdlib.h>
 #define mbedtls_printf     printf
 #define mbedtls_time_t     time_t
 #endif