--- antlr3-3.5.3/tool/src/main/antlr3/org/antlr/grammar/v3/CodeGenTreeWalker.g	2023-09-15 17:54:38.044172037 +0200
+++ antlr3-3.5.3/tool/src/main/antlr3/org/antlr/grammar/v3/CodeGenTreeWalker.g	2023-09-15 17:58:10.758972706 +0200
@@ -56,6 +56,7 @@
 import java.util.HashSet;
 import java.util.Set;
 import java.util.Collection;
+import java.util.Collections;
 import org.antlr.runtime.BitSet;
 import org.antlr.runtime.DFA;
 import org.stringtemplate.v4.ST;
@@ -284,6 +285,7 @@
         }
         labels.add( label );
     }
+    Collections.sort(labels); // ensure reproducible order
     return labels;
 }