diff --git a/tests/pthread_test.cpp b/tests/pthread_test.cpp
index 589cab4..d9b2523 100755
--- a/tests/pthread_test.cpp
+++ b/tests/pthread_test.cpp
@@ -926,7 +926,7 @@
   pthread_rwlock_t lock;
 
  public:
-  RwlockKindTestHelper(int kind_type) {
+  explicit RwlockKindTestHelper(int kind_type) {
     InitRwlock(kind_type);
   }
 
@@ -1539,7 +1539,7 @@
 struct PthreadMutex {
   pthread_mutex_t lock;
 
-  PthreadMutex(int mutex_type) {
+  explicit PthreadMutex(int mutex_type) {
     init(mutex_type);
   }
 
@@ -1640,7 +1640,7 @@
   }
 
  public:
-  MutexWakeupHelper(int mutex_type) : m(mutex_type) {
+  explicit MutexWakeupHelper(int mutex_type) : m(mutex_type) {
   }
 
   void test() {