diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index ecdd4f6..9f55db4 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -4771,11 +4771,11 @@
     return( ssl->dtls_srtp_info.chosen_dtls_srtp_profile);
 }
 
-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 ) {
     *key_len = 0;
 
     /* check output buffer size */
-    if ( key_buffer_len < ssl->dtls_srtp_info.dtls_srtp_keys_len) {
+    if ( *key_len < ssl->dtls_srtp_info.dtls_srtp_keys_len) {
         return MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL;
     }