diff --git a/src/openssl.c b/src/openssl.c
index 175c939..7943a20 100644
--- a/src/openssl.c
+++ b/src/openssl.c
@@ -35,6 +35,7 @@
  * OF SUCH DAMAGE.
  */
 
+#include <string.h>
 #include "openssl.h"
 
 int _libssh2_rsa_new(libssh2_rsa_ctx **rsa,