diff --git a/include/etl/observer.h b/include/etl/observer.h
index a68fda28..3894c219 100644
--- a/include/etl/observer.h
+++ b/include/etl/observer.h
@@ -300,6 +300,8 @@ namespace etl
   {
   public:
 
+    virtual ~observer() = default;
+
     virtual void notification(T1) = 0;
   };
 
diff --git a/include/etl/visitor.h b/include/etl/visitor.h
index e36aa31b..4dc6d99a 100644
--- a/include/etl/visitor.h
+++ b/include/etl/visitor.h
@@ -74,7 +74,7 @@ namespace etl
   {
   public:
 
-    virtual ~visitable() {}
+    virtual ~visitable() = default;
 
     virtual void accept(T1&) = 0;
   };
@@ -173,7 +173,7 @@ namespace etl
   {
   public:
 
-    virtual ~visitor() {}
+    virtual ~visitor() = default;
 
     virtual void visit(T1&) = 0;
   };