diff --git a/libcurl_http_fetcher.h b/libcurl_http_fetcher.h
index c101d90..0e34f9d 100644
--- a/libcurl_http_fetcher.h
+++ b/libcurl_http_fetcher.h
@@ -82,7 +82,7 @@
 
 class LibcurlHttpFetcher : public HttpFetcher {
  public:
-  LibcurlHttpFetcher(HardwareInterface* hardware);
+  explicit LibcurlHttpFetcher(HardwareInterface* hardware);
 
   // Cleans up all internal state. Does not notify delegate
   ~LibcurlHttpFetcher() override;