diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 72ba687..de92897 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -3232,7 +3232,7 @@
  *
  * \return         0 on succes, MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL if the key buffer is too small to hold the generated key
  */
-int mbedtls_ssl_get_dtls_srtp_key_material( const mbedtls_ssl_context *ssl, unsigned char *key, const size_t key_buffer_len, size_t *key_len );
+int mbedtls_ssl_get_dtls_srtp_key_material( const mbedtls_ssl_context *ssl, unsigned char *key, size_t *key_len );
 #endif /* MBEDTLS_SSL_DTLS_SRTP */
 
 /**