diff --git a/ext/lexbor/lexbor/core/str.c b/ext/lexbor/lexbor/core/str.c
index 3b3c574f1d9..d11a08614dd 100644
--- a/ext/lexbor/lexbor/core/str.c
+++ b/ext/lexbor/lexbor/core/str.c
@@ -133,9 +133,9 @@ lexbor_str_append(lexbor_str_t *str, lexbor_mraw_t *mraw,
 {
     lxb_char_t *data_begin;
 
-	if (length == 0) {
-		return str->data;
-	}
+    if (length == 0) {
+        return str->data;
+    }
 
     lexbor_str_check_size_arg_m(str, lexbor_str_size(str),
                                 mraw, (length + 1), NULL);