diff --git a/src/tests/rsa_test.c b/src/tests/rsa_test.c
index c0d05d26..91066faa 100644
--- a/src/tests/rsa_test.c
+++ b/src/tests/rsa_test.c
@@ -34,6 +34,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 /* Forcibly enable assertions */
 #undef NDEBUG
 
+#include <string.h>
 #include <ipxe/crypto.h>
 #include <ipxe/rsa.h>
 #include <ipxe/md5.h>