diff --git a/src/Resource.h b/src/Resource.h
index 7d792494..e75b8718 100644
--- a/src/Resource.h
+++ b/src/Resource.h
@@ -29,7 +29,7 @@
 
 class Resource {
 public:
-  Resource(const std::string &file);
+  explicit Resource(const std::string &file);
   Resource();
   virtual ~Resource();