diff --git a/src/stores/timelineStore.ts b/src/stores/timelineStore.ts
index 8c4c857..ea79824 100644
--- a/src/stores/timelineStore.ts
+++ b/src/stores/timelineStore.ts
@@ -111,6 +111,10 @@ export const useTimelineStore = create<TimelineStore & TimelineActions>(
       console.log(`Timeline initialized for document ${documentId}`);
     },
 
+    setActiveDocument: (documentId: string) => {
+      set({ activeDocumentId: documentId });
+    },
+
     loadTimeline: (documentId: string, timeline: Timeline) => {
       set((state) => {
         const newTimelines = new Map(state.timelines);
diff --git a/src/stores/workspaceStore.test.ts b/src/stores/workspaceStore.test.ts
index e133a6b..dde5e87 100644
--- a/src/stores/workspaceStore.test.ts
+++ b/src/stores/workspaceStore.test.ts
@@ -25,6 +25,7 @@ vi.mock("./timelineStore", () => ({
     getState: () => ({
       timelines: new Map(),
       loadTimeline: vi.fn(),
+      setActiveDocument: vi.fn(),
       clearTimeline: vi.fn(),
     }),
   },
diff --git a/src/stores/workspaceStore.ts b/src/stores/workspaceStore.ts
index 1679816..bd45926 100644
--- a/src/stores/workspaceStore.ts
+++ b/src/stores/workspaceStore.ts
@@ -600,6 +600,11 @@ export const useWorkspaceStore = create<Workspace & WorkspaceActions>((set, get)
           activeDocumentId: documentId,
         };
       });
+
+      // Always sync timelineStore.activeDocumentId — loadDocument returns early
+      // when the document is already in memory, so loadTimeline is never called
+      // and timelineStore.activeDocumentId would remain stale.
+      useTimelineStore.getState().setActiveDocument(documentId);
     });
   },
 
diff --git a/src/types/timeline.ts b/src/types/timeline.ts
index 8d83034..85e63f4 100644
--- a/src/types/timeline.ts
+++ b/src/types/timeline.ts
@@ -66,6 +66,9 @@ export interface TimelineActions {
   // Load timeline from document
   loadTimeline: (documentId: string, timeline: Timeline) => void;
 
+  // Set active document without reloading timeline data (for switching between already-loaded documents)
+  setActiveDocument: (documentId: string) => void;
+
   // Create new state
   createState: (label: string, description?: string, cloneFromCurrent?: boolean) => StateId;