diff --git a/content/treestyletab/res/tabsDragUtils.js b/content/treestyletab/res/tabsDragUtils.js
index 25c6d57a..64fd098d 100644
--- a/content/treestyletab/res/tabsDragUtils.js
+++ b/content/treestyletab/res/tabsDragUtils.js
@@ -131,7 +131,9 @@
 						'if (!("animLastScreenX" in draggedTab._dragData))',
 						'let tabsWidth = 0;\n' +
 						'draggedTabs.forEach(function(draggedTab) {\n' +
-						'  tabsWidth += draggedTab.boxObject[size];\n' +
+						'  let style = window.getComputedStyle(draggedTab, null);\n' +
+						'  if (style.visibility != "collapse" && style.display != "none")\n' +
+						'    tabsWidth += draggedTab.boxObject[size];\n' +
 						'  window["piro.sakura.ne.jp"].tabsDragUtils.fixDragData(draggedTab._dragData);\n' +
 						'  $&'
 					).replace(
@@ -219,7 +221,8 @@
 // 
 // let tabsWidth = 0;
 // draggedTabs.forEach(function(draggedTab) {
-// tabsWidth += draggedTab.boxObject[size]/*.width*/;
+// let style = window.getComputedStyle(draggedTab, null);
+// if (style.visibility != "collapse" && style.display != "none") tabsWidth += draggedTab.boxObject[size]/*.width*/;
 // window['piro.sakura.ne.jp'].tabsDragUtils.fixDragData(draggedTab._dragData);
 //           if (!("animLastScreenX" in draggedTab._dragData))
 //             draggedTab._dragData.animLastScreenX = draggedTab._dragData[position]/*.screenX*/;
diff --git a/modules/tabbarDNDObserver.js b/modules/tabbarDNDObserver.js
index 770eb4e9..3163ded8 100644
--- a/modules/tabbarDNDObserver.js
+++ b/modules/tabbarDNDObserver.js
@@ -996,15 +996,13 @@ catch(e) {
 		if (tabbar._tabDropIndicator)
 			tabbar._tabDropIndicator.collapsed = true;
 
-		var draggedTab;
-		if (dt.dropEffect != 'link') {
-			draggedTab = dt.mozGetDataAt(TAB_DROP_TYPE, 0);
-			if (!draggedTab) {
-				aEvent.stopPropagation();
-				return;
-			}
-			draggedTab.style.opacity = '';
+		var draggedTab = dt.mozGetDataAt(TAB_DROP_TYPE, 0);
+		if (dt.dropEffect != 'link' && !draggedTab) {
+			aEvent.stopPropagation();
+			return;
 		}
+		if (draggedTab)
+			draggedTab.style.opacity = '';
 
 		var sourceBrowser = sv.getTabBrowserFromChild(draggedTab);
 		if (draggedTab && sourceBrowser != b)