From ae10f58dc456a954d06ecc57376c8e77e9b243ae Mon Sep 17 00:00:00 2001
From: Frederik Seiffert <frederik@algoriddim.com>
Date: Mon, 12 Aug 2019 19:30:25 +0200
Subject: [PATCH] Fixed NSOperation calling removeObserver more than once.

This would cause an error if/when -removeObserver:forKeyPath: is implemented to throw an error when unregistering non-registered observers.
---
 Source/NSOperation.m | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/Source/NSOperation.m b/Source/NSOperation.m
index 89e5f059e..6a7cc8aee 100644
--- a/Source/NSOperation.m
+++ b/Source/NSOperation.m
@@ -206,7 +206,10 @@ static NSArray	*empty = nil;
     {
       NSOperation	*op;
 
-      [self removeObserver: self forKeyPath: @"isFinished"];
+      if (!internal->finished)
+        {
+          [self removeObserver: self forKeyPath: @"isFinished"];
+        }
       while ((op = [internal->dependencies lastObject]) != nil)
 	{
 	  [self removeDependency: op];