diff --git a/modules/browser.js b/modules/browser.js
index 1949e2be..d9a0657b 100644
--- a/modules/browser.js
+++ b/modules/browser.js
@@ -5785,7 +5785,7 @@ TreeStyleTabBrowser.prototype = {
 		aTab.removeAttribute(this.kX_OFFSET);
 		aTab.removeAttribute(this.kY_OFFSET);
 
-		if (!this.canCollapseSubtree(this.getParentTab(aTab)))
+		if (!this.canCollapseSubtree(this.getRootTab(aTab)))
 			aCollapsed = false;
 
 		aTab.setAttribute(this.kCOLLAPSING_PHASE, aCollapsed ? this.kCOLLAPSING_PHASE_TO_BE_COLLAPSED : this.kCOLLAPSING_PHASE_TO_BE_EXPANDED );