diff --git a/CHANGELOG.md b/CHANGELOG.md
index e8c2139f9..af63c2aea 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,7 @@ All notable changes to this project will be documented in this file.
 - [#1863] Export to PDF - cannot read fonts with long CMAP
 - Go to document class when switched to tag list view
 - Copy/Move with dependencies order of tags
+- [#1865] ConcurrentModificationException on SWF close
 
 ## [16.2.0] - 2022-11-08
 ### Added
@@ -2549,6 +2550,7 @@ All notable changes to this project will be documented in this file.
 [#1701]: https://www.free-decompiler.com/flash/issues/1701
 [#1864]: https://www.free-decompiler.com/flash/issues/1864
 [#1863]: https://www.free-decompiler.com/flash/issues/1863
+[#1865]: https://www.free-decompiler.com/flash/issues/1865
 [#1414]: https://www.free-decompiler.com/flash/issues/1414
 [#1755]: https://www.free-decompiler.com/flash/issues/1755
 [#1460]: https://www.free-decompiler.com/flash/issues/1460
diff --git a/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/tags/base/ButtonTag.java b/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/tags/base/ButtonTag.java
index aabe7d313..9269778f9 100644
--- a/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/tags/base/ButtonTag.java
+++ b/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/tags/base/ButtonTag.java
@@ -108,6 +108,9 @@ public abstract class ButtonTag extends DrawableTag implements Timelined {
     }
 
     public DefineButtonSoundTag getSounds() {
+        if (swf == null) {
+            return null;
+        }
         return (DefineButtonSoundTag) swf.getCharacterIdTag(getCharacterId(), DefineButtonSoundTag.ID);
     }
 
diff --git a/src/com/jpexs/decompiler/flash/gui/MainPanel.java b/src/com/jpexs/decompiler/flash/gui/MainPanel.java
index 11ca29416..57bd09b88 100644
--- a/src/com/jpexs/decompiler/flash/gui/MainPanel.java
+++ b/src/com/jpexs/decompiler/flash/gui/MainPanel.java
@@ -4942,7 +4942,8 @@ public final class MainPanel extends JPanel implements TreeSelectionListener, Se
     }
 
     private static void calculateMissingNeededCharacters(Map<TreeItem, Set<Integer>> missingNeededCharacters, Timelined tim) {
-        for (Tag t : tim.getTags()) {
+        List<Tag> tags = tim.getTags().toArrayList();
+        for (Tag t : tags) {
             missingNeededCharacters.put(t, t.getMissingNeededCharacters());
             if (t instanceof DefineSpriteTag) {
                 calculateMissingNeededCharacters(missingNeededCharacters, (DefineSpriteTag) t);