diff --git a/lib/hcrypto/des.c b/lib/hcrypto/des.c
index 9f5c648ec..ac174180f 100644
--- a/lib/hcrypto/des.c
+++ b/lib/hcrypto/des.c
@@ -728,6 +728,7 @@ DES_cfb64_encrypt(const void *in, void *out,
 	int i = *num;
 	unsigned char c;
 
+	memset(tmp, 0, DES_CBLOCK_LEN);
 	while (length > 0) {
 	    if (i == 0) {
 		DES_encrypt(uiv, ks, 1);