diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index f6b56f1..9a66984 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -4717,7 +4717,7 @@
 
 int mbedtls_ssl_dtls_srtp_set_mki_value( mbedtls_ssl_context *ssl,
                                          unsigned char *mki_value,
-                                         size_t mki_len )
+                                         uint16_t mki_len )
 {
     if ( mki_len > MBEDTLS_TLS_SRTP_MAX_MKI_LENGTH )
     {