diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 0dd4a6c..8604997 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -1484,7 +1484,7 @@
         unsigned char add_data[13];
         unsigned char taglen = ssl->transform_in->ciphersuite_info->flags &
                                POLARSSL_CIPHERSUITE_SHORT_TAG ? 8 : 16;
-        unsigned char explicit_iv_len =  ssl->transform_in->ivlen -
+        size_t explicit_iv_len =  ssl->transform_in->ivlen -
                                          ssl->transform_in->fixed_ivlen;
 
         if( ssl->in_msglen < (size_t) explicit_iv_len + taglen )