diff --git a/tests/libs/thread_local_dtor.cpp b/tests/libs/thread_local_dtor.cpp
index cefff7a..90fd418 100644
--- a/tests/libs/thread_local_dtor.cpp
+++ b/tests/libs/thread_local_dtor.cpp
@@ -30,7 +30,7 @@
 
 class TestClass {
  public:
-  TestClass(bool* flag) : flag_(flag) {}
+  explicit TestClass(bool* flag) : flag_(flag) {}
   ~TestClass() {
     *flag_ = true;
   }
diff --git a/tests/libs/thread_local_dtor2.cpp b/tests/libs/thread_local_dtor2.cpp
index 9b2b164..177c91b 100644
--- a/tests/libs/thread_local_dtor2.cpp
+++ b/tests/libs/thread_local_dtor2.cpp
@@ -30,7 +30,7 @@
 
 class TestClass {
  public:
-  TestClass(bool* flag) : flag_(flag) {}
+  explicit TestClass(bool* flag) : flag_(flag) {}
   ~TestClass() {
     *flag_ = true;
   }