diff --git a/src/dex2oat.cc b/src/dex2oat.cc
index 971fc09..096c694 100644
--- a/src/dex2oat.cc
+++ b/src/dex2oat.cc
@@ -217,7 +217,7 @@
 
  private:
 
-  Dex2Oat(Runtime* runtime) : runtime_(runtime) {}
+  explicit Dex2Oat(Runtime* runtime) : runtime_(runtime) {}
 
   static Runtime* CreateRuntime(Runtime::Options& options) {
     Runtime* runtime = Runtime::Create(options, false);