diff --git a/languagetool-http-client/src/main/java/org/languagetool/remote/ArtificialErrorEval.java b/languagetool-http-client/src/main/java/org/languagetool/remote/ArtificialErrorEval.java
index f5de62d62ea1..f50c53206fce 100644
--- a/languagetool-http-client/src/main/java/org/languagetool/remote/ArtificialErrorEval.java
+++ b/languagetool-http-client/src/main/java/org/languagetool/remote/ArtificialErrorEval.java
@@ -794,7 +794,7 @@ private static List<String> differences(String s1, String s2) {
       fromStart++;
     }
     int fromEnd = 0;
-    while (s1.charAt(l1 - 1 - fromEnd) == s2.charAt(l2 - 1 - fromEnd)) {
+    while (fromEnd < l1 && fromEnd < l2 && s1.charAt(l1 - 1 - fromEnd) == s2.charAt(l2 - 1 - fromEnd)) {
       fromEnd++;
     }
     // corrections (e.g. stress vs stresses)