diff --git a/src/protocols/AFSK/AFSK.h b/src/protocols/AFSK/AFSK.h
index d4ca58d6..e38b5b76 100644
--- a/src/protocols/AFSK/AFSK.h
+++ b/src/protocols/AFSK/AFSK.h
@@ -26,7 +26,7 @@ class AFSKClient  {
       \brief Copy contructor.
       \param aud Pointer to the AFSKClient instance to copy.
     */
-    AFSKClient(AFSKClient* aud);
+    explicit AFSKClient(AFSKClient* aud);
 
     /*!
       \brief Initialization method.