diff --git a/Parser/tokenizer.c b/Parser/tokenizer.c
index 6b37b31..b1a9ee1 100644
--- a/Parser/tokenizer.c
+++ b/Parser/tokenizer.c
@@ -503,7 +503,7 @@
 	if (!check_bom(buf_getc, buf_ungetc, buf_setreadl, tok))
 		return NULL;
 	str = tok->str;		/* string after BOM if any */
-	assert(r);
+	assert(str);
 	if (tok->enc != NULL) {
 		utf8 = translate_into_utf8(str, tok->enc);
 		if (utf8 == NULL)