diff --git a/src/crypto/sha1-tprf.c b/src/crypto/sha1-tprf.c
index a52949462..562510f89 100644
--- a/src/crypto/sha1-tprf.c
+++ b/src/crypto/sha1-tprf.c
@@ -66,5 +66,7 @@ int sha1_t_prf(const u8 *key, size_t key_len, const char *label,
 		len[0] = SHA1_MAC_LEN;
 	}
 
+	os_memset(hash, 0, SHA1_MAC_LEN);
+
 	return 0;
 }