diff --git a/src/main/java/proteomics/ECL2.java b/src/main/java/proteomics/ECL2.java
index cf527bb..4dbf9ae 100644
--- a/src/main/java/proteomics/ECL2.java
+++ b/src/main/java/proteomics/ECL2.java
@@ -137,6 +137,9 @@ private ECL2(String parameter_path, String spectra_path) throws IOException, MzX
         if (thread_num == 0) {
             thread_num = 1 + Runtime.getRuntime().availableProcessors();
         }
+        if (debug) {
+            thread_num = 1;
+        }
         ExecutorService thread_pool = Executors.newFixedThreadPool(thread_num);
         Search search_obj = new Search(build_index_obj, parameter_map);
         List<Future<FinalResultEntry>> taskList = new LinkedList<>();