diff --git a/crypto/conf/conf_api.c b/crypto/conf/conf_api.c
index 909d72b4b..17bae8359 100644
--- a/crypto/conf/conf_api.c
+++ b/crypto/conf/conf_api.c
@@ -64,6 +64,7 @@
 #endif
 
 #include <assert.h>
+#include <stdlib.h>
 #include <string.h>
 #include <openssl/conf.h>
 #include <openssl/conf_api.h>