diff --git a/tests/controls/treectrltest.cpp b/tests/controls/treectrltest.cpp
index 65e71e9bda..0f49ca298c 100644
--- a/tests/controls/treectrltest.cpp
+++ b/tests/controls/treectrltest.cpp
@@ -34,7 +34,7 @@
 class TreeCtrlTestCase
 {
 public:
-    TreeCtrlTestCase(int exStyle = 0)
+    explicit TreeCtrlTestCase(int exStyle = 0)
     {
         m_tree = new wxTreeCtrl(wxTheApp->GetTopWindow(),
                                 wxID_ANY,