1 files changed, 1 insertions, 1 deletions
diff --git a/string.c b/string.c
index 983c2a1166..7f29cea2b6 100644
--- a/string.c
+++ b/string.c
@@ -2098,7 +2098,7 @@ str_buf_cat(VALUE str, const char *ptr, long len)
     if (capa <= total) {
 	while (total > capa) {
 	    if (capa + termlen >= LONG_MAX / 2) {
-		capa = (total + 4095) / 4096;
+		capa = (total + 4095) / 4096 * 4096;
 		break;
 	    }
 	    capa = (capa + termlen) * 2;