diff --git a/third_party/srtp/crypto/cipher/cipher.c b/third_party/srtp/crypto/cipher/cipher.c
index b5ef164..489a52d 100644
--- a/third_party/srtp/crypto/cipher/cipher.c
+++ b/third_party/srtp/crypto/cipher/cipher.c
@@ -269,7 +269,7 @@
   
   for (j=0; j < NUM_RAND_TESTS; j++) {
     unsigned length;
-    int plaintext_len;
+    unsigned plaintext_len;
     uint8_t key[MAX_KEY_LEN];
     uint8_t  iv[MAX_KEY_LEN];