diff --git a/helpers/rust/src/main.rs b/helpers/rust/src/main.rs
index ad875bc..fbc819b 100644
--- a/helpers/rust/src/main.rs
+++ b/helpers/rust/src/main.rs
@@ -166,6 +166,8 @@ fn main() {
     )
     .init();
 
+    log::info!("Log level set to {}", log::max_level());
+
     if cli.no_derived && cli.only == Some(Action::Derived) {
         log::error!("--no-derived and --only=derived are mutually exclusive");
         std::process::exit(1);
diff --git a/helpers/rust/src/types/statistics.rs b/helpers/rust/src/types/statistics.rs
index a8c59cf..dba1db9 100644
--- a/helpers/rust/src/types/statistics.rs
+++ b/helpers/rust/src/types/statistics.rs
@@ -75,6 +75,8 @@ impl DumpStatistics {
     }
 
     fn close_subclasses(&mut self) -> usize {
+        log::info!("Computing subclass closure");
+
         let mut added = 0;
         let direct_superclasses = self
             .classes
@@ -85,6 +87,7 @@ impl DumpStatistics {
 
         while let Some(class) = class_queue.pop_front() {
             let record = self.classes.entry(class).or_default();
+            let mut done = HashSet::new();
             let mut superclasses = record
                 .direct_superclasses
                 .iter()
@@ -93,10 +96,16 @@ impl DumpStatistics {
 
             while let Some(superclass) = superclasses.pop_front() {
                 record.superclasses.insert(superclass);
+                done.insert(superclass);
                 added += 1;
 
                 if let Some(new_superclasses) = direct_superclasses.get(&superclass) {
-                    superclasses.extend(new_superclasses.iter().cloned());
+                    superclasses.extend(
+                        new_superclasses
+                            .iter()
+                            .filter(|superclass| !done.contains(superclass))
+                            .cloned(),
+                    );
                 }
             }
         }
@@ -116,6 +125,8 @@ impl DumpStatistics {
             })
             .collect::<Vec<_>>();
 
+        log::info!("Found {} non-empty classes", classes.len());
+
         for (class, superclasses) in classes {
             for super_class in superclasses {
                 let record = self.classes.entry(super_class).or_default();