diff --git a/src/model/OptionManager.ts b/src/model/OptionManager.ts
index 846d3c2157..973b73b4aa 100644
--- a/src/model/OptionManager.ts
+++ b/src/model/OptionManager.ts
@@ -314,7 +314,7 @@ function parseRawOption(
     if (declaredBaseOption) {
         baseOption = declaredBaseOption;
         // For merge option.
-        if (!baseOption.timeline) {
+        if (!baseOption.timeline && timelineOnRoot) {
             baseOption.timeline = timelineOnRoot;
         }
     }