diff --git a/packages/mindplot/src/components/Designer.ts b/packages/mindplot/src/components/Designer.ts
index b5a66ef6..e85f2e14 100644
--- a/packages/mindplot/src/components/Designer.ts
+++ b/packages/mindplot/src/components/Designer.ts
@@ -137,8 +137,8 @@ class Designer extends Events {
   }
 
   private _registerWheelEvents(): void {
-    const zoomFactor = 1.006;
-    document.addEventListener('wheel', (event) => {
+    const zoomFactor = 1.02;
+    document.addEventListener('wheel', (event: WheelEvent) => {
       if (event.deltaX > 0 || event.deltaY > 0) {
         this.zoomOut(zoomFactor);
       } else {
diff --git a/packages/mindplot/src/components/RelationshipPivot.ts b/packages/mindplot/src/components/RelationshipPivot.ts
index 32153ae4..ade7a4d4 100644
--- a/packages/mindplot/src/components/RelationshipPivot.ts
+++ b/packages/mindplot/src/components/RelationshipPivot.ts
@@ -28,7 +28,7 @@ class RelationshipPivot {
 
   private _designer: Designer;
 
-  private _mouseMoveEvent: MouseEvent;
+  private _mouseMoveEvent;
 
   private _onClickEvent: (event: MouseEvent) => void;
 
diff --git a/packages/mindplot/src/components/Workspace.ts b/packages/mindplot/src/components/Workspace.ts
index f49da29d..b764c1f9 100644
--- a/packages/mindplot/src/components/Workspace.ts
+++ b/packages/mindplot/src/components/Workspace.ts
@@ -113,11 +113,11 @@ class Workspace {
     }
   }
 
-  addEvent(type: string, listener): void {
+  addEvent(type: string, listener: (event: Event) => void): void {
     this._workspace.addEvent(type, listener);
   }
 
-  removeEvent(type: string, listener): void {
+  removeEvent(type: string, listener: (event: Event) => void): void {
     $assert(type, 'type can not be null');
     $assert(listener, 'listener can not be null');
     this._workspace.removeEvent(type, listener);
@@ -193,7 +193,7 @@ class Workspace {
     const workspace = this._workspace;
     const screenManager = this._screenManager;
     const mWorkspace = this;
-    const mouseDownListener = function mouseDownListener(event) {
+    const mouseDownListener = function mouseDownListener(event: MouseEvent) {
       if (!$defined(workspace._mouseMoveListener)) {
         if (mWorkspace.isWorkspaceEventsEnabled()) {
           mWorkspace.enableWorkspaceEvents(false);
@@ -202,7 +202,7 @@ class Workspace {
           const originalCoordOrigin = workspace.getCoordOrigin();
 
           let wasDragged = false;
-          workspace._mouseMoveListener = (mouseMoveEvent) => {
+          workspace._mouseMoveListener = (mouseMoveEvent: MouseEvent) => {
             const currentMousePosition = screenManager.getWorkspaceMousePosition(mouseMoveEvent);
 
             const offsetX = currentMousePosition.x - mouseDownPosition.x;
diff --git a/packages/mindplot/src/components/commands/DragTopicCommand.ts b/packages/mindplot/src/components/commands/DragTopicCommand.ts
index 8bee475c..8e3766ef 100644
--- a/packages/mindplot/src/components/commands/DragTopicCommand.ts
+++ b/packages/mindplot/src/components/commands/DragTopicCommand.ts
@@ -76,7 +76,7 @@ class DragTopicCommand extends Command {
     }
 
     // Finally, connect topic ...
-    if (origParentTopic.getId() !== this._parentId) {
+    if (!$defined(origParentTopic) || origParentTopic.getId() !== this._parentId) {
       if ($defined(this._parentId)) {
         const parentTopic = commandContext.findTopics([this._parentId])[0];
         commandContext.connect(topic, parentTopic);