diff --git a/CHANGELOG.md b/CHANGELOG.md
index 74523da1a..ce2105a73 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,9 @@ All notable changes to this project will be documented in this file.
 - [#1485] Improved skins support, night mode
 - [#1681] AS3 - context menu for adding classes on packages
 
+### Fixed
+- [#1687] Slow speed of cyclic tags detection
+
 ## [14.4.0] - 2021-04-05
 ### Added
 - [#1015], [#1466], [#1513] Better error messages during saving, display message on out of memory
@@ -2192,6 +2195,7 @@ All notable changes to this project will be documented in this file.
 [alpha 7]: https://github.com/jindrapetrik/jpexs-decompiler/releases/tag/alpha7
 [#1485]: https://www.free-decompiler.com/flash/issues/1485
 [#1681]: https://www.free-decompiler.com/flash/issues/1681
+[#1687]: https://www.free-decompiler.com/flash/issues/1687
 [#1015]: https://www.free-decompiler.com/flash/issues/1015
 [#1466]: https://www.free-decompiler.com/flash/issues/1466
 [#1513]: https://www.free-decompiler.com/flash/issues/1513
diff --git a/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/SWF.java b/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/SWF.java
index ba0cc8ef5..54fa04d04 100644
--- a/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/SWF.java
+++ b/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/SWF.java
@@ -359,6 +359,8 @@ public final class SWF implements SWFContainerItem, Timelined {
     @Internal
     private Map<String, ASMSource> asmsCache;
 
+    private Set<Integer> cyclicCharacters = null;
+
     private static final DecompilerPool decompilerPool = new DecompilerPool();
 
     public static final String AS2_PKG_PREFIX = "__Packages.";
@@ -2653,6 +2655,7 @@ public final class SWF implements SWFContainerItem, Timelined {
         characters = null;
         characterIdTags = null;
         timeline = null;
+        cyclicCharacters = null;
         clearReadOnlyListCache();
         clearImageCache();
         clearScriptCache();
@@ -3842,4 +3845,54 @@ public final class SWF implements SWFContainerItem, Timelined {
     public RECT getRectWithStrokes() {
         return getRect();
     }
+
+    public Set<Integer> getCyclicCharacters() {
+        if (cyclicCharacters != null) {
+            return cyclicCharacters;
+        }
+        Set<Integer> ct = new HashSet<>();
+        Map<Integer, Set<Integer>> characterToNeeded = new HashMap<>();
+
+        for (Tag t : getTags()) {
+            if (t instanceof CharacterTag) {
+                CharacterTag cht = (CharacterTag) t;
+                Set<Integer> needed = new HashSet<>();
+                cht.getNeededCharacters(needed);
+                characterToNeeded.put(cht.getCharacterId(), needed);
+            }
+        }
+
+        for (int chid : characterToNeeded.keySet()) {
+            for (int n : characterToNeeded.get(chid)) {
+                if (searchNeeded(characterToNeeded, chid, n, new HashSet<>())) {
+                    ct.add(chid);
+                }
+            }
+        }
+
+        cyclicCharacters = ct;
+        return cyclicCharacters;
+    }
+
+    private boolean searchNeeded(Map<Integer, Set<Integer>> characterToNeeded, int searched, int current, Set<Integer> visited) {
+        if (visited.contains(current)) {
+            return false;
+        }
+        visited.add(current);
+        if (current == searched) {
+            return true;
+        }
+
+        if (!characterToNeeded.containsKey(current)) {
+            return false;
+        }
+
+        for (int n : characterToNeeded.get(current)) {
+            if (searchNeeded(characterToNeeded, searched, n, visited)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
 }
diff --git a/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/timeline/Timeline.java b/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/timeline/Timeline.java
index e50d8e59e..72b6178da 100644
--- a/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/timeline/Timeline.java
+++ b/libsrc/ffdec_lib/src/com/jpexs/decompiler/flash/timeline/Timeline.java
@@ -323,8 +323,7 @@ public class Timeline {
                 }
                 CharacterTag character = swf.getCharacter(characterId);
                 if (character instanceof DefineSpriteTag) {
-                    Stack<Integer> cyStack = new Stack<>();
-                    if (isCyclic(timelined, cyStack)) {
+                    if (swf.getCyclicCharacters().contains(characterId)) {
                         fl.characterId = -1;
                     }
                 }
@@ -1393,28 +1392,4 @@ public class Timeline {
 
         return false;
     }
-
-    private boolean isCyclic(Timelined tim, Stack<Integer> walked) {
-        for (Tag t : tim.getTags()) {
-            if (t instanceof PlaceObjectTypeTag) {
-                PlaceObjectTypeTag p = (PlaceObjectTypeTag) t;
-                int chid = p.getCharacterId();
-                if (chid != -1) {
-                    if (walked.contains(chid)) {
-                        return true;
-                    }
-                    CharacterTag character = swf.getCharacter(chid);
-                    if (character instanceof DefineSpriteTag) {
-                        walked.push(chid);
-                        if (isCyclic((DefineSpriteTag) character, walked)) {
-                            walked.pop();
-                            return true;
-                        }
-                        walked.pop();
-                    }
-                }
-            }
-        }
-        return false;
-    }
 }