diff --git a/src/AppleMessageDigestImpl.cc b/src/AppleMessageDigestImpl.cc
index 1498f075..7d8eafb1 100644
--- a/src/AppleMessageDigestImpl.cc
+++ b/src/AppleMessageDigestImpl.cc
@@ -49,6 +49,7 @@ template<size_t dlen,
 class MessageDigestBase : public MessageDigestImpl {
 public:
   MessageDigestBase() { reset(); }
+  virtual ~MessageDigestBase() {}
 
   virtual size_t getDigestLength() const {
     return dlen;
diff --git a/src/AppleMessageDigestImpl.h b/src/AppleMessageDigestImpl.h
index b3851da5..91992603 100644
--- a/src/AppleMessageDigestImpl.h
+++ b/src/AppleMessageDigestImpl.h
@@ -45,6 +45,7 @@ namespace aria2 {
 
 class MessageDigestImpl {
 public:
+  virtual ~MessageDigestImpl() {}
   static SharedHandle<MessageDigestImpl> sha1();
   static SharedHandle<MessageDigestImpl> create(const std::string& hashType);