diff --git a/library/aes.c b/library/aes.c
index 3666030..a186dee 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -1222,7 +1222,9 @@
     int ret = 0, i, j, u, v;
     unsigned char key[32];
     unsigned char buf[64];
+#if defined(MBEDTLS_CIPHER_MODE_CBC) || defined(MBEDTLS_CIPHER_MODE_CFB)
     unsigned char iv[16];
+#endif
 #if defined(MBEDTLS_CIPHER_MODE_CBC)
     unsigned char prv[16];
 #endif