diff --git a/image_verify.hpp b/image_verify.hpp
index 88762e1..8cda65c 100644
--- a/image_verify.hpp
+++ b/image_verify.hpp
@@ -49,7 +49,7 @@
      *
      *  @param[in] fd - File descriptor
      */
-    CustomFd(int fd) : fd(fd)
+    explicit CustomFd(int fd) : fd(fd)
     {}
 
     ~CustomFd()