diff --git a/src/libgrand-search-daemon/utils/chineseletterhelper.cpp b/src/libgrand-search-daemon/utils/chineseletterhelper.cpp
index 59613bec..d054d025 100644
--- a/src/libgrand-search-daemon/utils/chineseletterhelper.cpp
+++ b/src/libgrand-search-daemon/utils/chineseletterhelper.cpp
@@ -24,6 +24,8 @@ ChineseLetterHelper::ChineseLetterHelper()
 
 bool ChineseLetterHelper::chinese2Pinyin(const QString &words, QString &result)
 {
+    QReadLocker lk(&m_lock);
+
     int ok = false;
     for (int i = 0; i < words.length(); ++i) {
         const uint key = words.at(i).unicode();
@@ -42,6 +44,13 @@ bool ChineseLetterHelper::chinese2Pinyin(const QString &words, QString &result)
 
 void ChineseLetterHelper::initDict()
 {
+    // fast check
+    if (m_inited)
+        return;
+
+    QWriteLocker lk(&m_lock);
+
+    // check again, m_inited may be setted to true in other thread.
     if (m_inited)
         return;
 
diff --git a/src/libgrand-search-daemon/utils/chineseletterhelper.h b/src/libgrand-search-daemon/utils/chineseletterhelper.h
index 8e0079fb..74b4b49e 100644
--- a/src/libgrand-search-daemon/utils/chineseletterhelper.h
+++ b/src/libgrand-search-daemon/utils/chineseletterhelper.h
@@ -7,6 +7,7 @@
 
 #include <QHash>
 #include <QObject>
+#include <QReadWriteLock>
 
 #define Ch2PyIns GrandSearch::ChineseLetterHelper::instance()
 
@@ -24,6 +25,7 @@ class ChineseLetterHelper
     void initDict();
     volatile bool m_inited = false;
     QHash<uint, QString> m_dict;
+    QReadWriteLock m_lock;
 };
 
 }