diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4ce15bdc8..977ad7149 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,7 +14,8 @@ All notable changes to this project will be documented in this file.
 - Improper standalone layer termination, not cleaning temp files
 - [#2636] ActionScript - Incorrect always-break detection causing insertion of while(true)
 - ActionScript - newline after do..while
-- StackOverflow on cyclic buttons
+- StackOverflow on cyclic characters
+- ConcurrentModification in abc indexing
 
 ## [25.0.0] - 2026-02-10
 ### Added
diff --git a/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/abc/avm2/parser/script/AbcIndexing.java b/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/abc/avm2/parser/script/AbcIndexing.java
index b636b96e2..315f1d28a 100644
--- a/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/abc/avm2/parser/script/AbcIndexing.java
+++ b/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/abc/avm2/parser/script/AbcIndexing.java
@@ -581,7 +581,7 @@ public final class AbcIndexing {
     /**
      * Rebuilds package to objects name map.
      */
-    public void rebuildPkgToObjectsNameMap() {
+    public synchronized void rebuildPkgToObjectsNameMap() {
         pkgToObjectsName.clear();
         Set<ClassDef> cs = new LinkedHashSet<>(classes.keySet());
         for (ClassDef cd : cs) {
@@ -1119,7 +1119,7 @@ public final class AbcIndexing {
      *
      * @param abc ABC to add
      */
-    public void addAbc(ABC abc) {
+    public synchronized void addAbc(ABC abc) {
         if (abc == null) {
             return;
         }