diff --git a/debug_counter.h b/debug_counter.h
index e569b18983..daa46fdcbf 100644
--- a/debug_counter.h
+++ b/debug_counter.h
@@ -263,6 +263,11 @@ RB_DEBUG_COUNTER(mjit_exec_not_added_add_iseq)
 RB_DEBUG_COUNTER(mjit_exec_not_ready)
 RB_DEBUG_COUNTER(mjit_exec_not_compiled)
 
+/* rb_mjit_unit_list length */
+RB_DEBUG_COUNTER(mjit_length_unit_queue)
+RB_DEBUG_COUNTER(mjit_length_active_units)
+RB_DEBUG_COUNTER(mjit_length_compact_units)
+
 /* load (not implemented yet) */
 /*
 RB_DEBUG_COUNTER(load_files)
diff --git a/mjit.c b/mjit.c
index a1c8f238c2..710f370947 100644
--- a/mjit.c
+++ b/mjit.c
@@ -781,6 +781,12 @@ mjit_finish(bool close_handle_p)
     if (!mjit_enabled)
         return;
 
+#if USE_DEBUG_COUNTER
+    rb_debug_counter_add(RB_DEBUG_COUNTER_mjit_length_unit_queue, unit_queue.length, 1);
+    rb_debug_counter_add(RB_DEBUG_COUNTER_mjit_length_active_units, active_units.length, 1);
+    rb_debug_counter_add(RB_DEBUG_COUNTER_mjit_length_compact_units, compact_units.length, 1);
+#endif
+
     /* Wait for pch finish */
     verbose(2, "Stopping worker thread");
     CRITICAL_SECTION_START(3, "in mjit_finish to wakeup from pch");