diff --git a/src/pixi/display/DisplayObjectContainer.js b/src/pixi/display/DisplayObjectContainer.js
index fc8841a..9824471 100644
--- a/src/pixi/display/DisplayObjectContainer.js
+++ b/src/pixi/display/DisplayObjectContainer.js
@@ -217,9 +217,13 @@
 	if (child === child2) {
 		return;
 	}
-	
+
 	var index1 = this.children.indexOf(child);
 	var index2 = this.children.indexOf(child2);
+	
+	if (index1 < 0 || index2 < 0) {
+		throw new Error("swapChildren: Both the supplied DisplayObjects must be a child of the caller.");
+	}
 
 	this.removeChild(child);
 	this.removeChild(child2);