diff --git a/boot/bootutil/src/image_rsa.c b/boot/bootutil/src/image_rsa.c
index 7b1f4d4..4890f46 100644
--- a/boot/bootutil/src/image_rsa.c
+++ b/boot/bootutil/src/image_rsa.c
@@ -17,6 +17,8 @@
  * under the License.
  */
 
+#include <string.h>
+
 #include "syscfg/syscfg.h"
 
 #if MYNEWT_VAL(BOOTUTIL_SIGN_RSA)