diff --git a/Source/NSOutlineView.m b/Source/NSOutlineView.m
index 5e6a63af6..336cd662a 100644
--- a/Source/NSOutlineView.m
+++ b/Source/NSOutlineView.m
@@ -521,6 +521,9 @@ static NSImage *unexpandable  = nil;
  */
 - (int)rowForItem: (id)item
 {
+  if(item == nil)
+    return -1;
+
   int row = [_items indexOfObject: item];
   return (row == NSNotFound) ? -1 : row;
 }