diff --git a/include/exiv2/xmp_exiv2.hpp b/include/exiv2/xmp_exiv2.hpp
index af8d092c..ec3d02c6 100644
--- a/include/exiv2/xmp_exiv2.hpp
+++ b/include/exiv2/xmp_exiv2.hpp
@@ -10,6 +10,8 @@
 #include "metadatum.hpp"
 #include "properties.hpp"
 
+#include <functional>
+
 // *****************************************************************************
 // namespace extensions
 namespace Exiv2 {
@@ -312,7 +314,7 @@ class EXIV2API XmpParser {
     @param pLockData Pointer to the pLockData passed to initialize()
     @param lockUnlock Indicates whether to lock (true) or unlock (false)
    */
-  using XmpLockFct = void (*)(void* pLockData, bool lockUnlock);
+  using XmpLockFct = std::function<void(void* pLockData, bool lockUnlock)>;
 
   /*!
     @brief Initialize the XMP Toolkit.
diff --git a/src/crwimage_int.hpp b/src/crwimage_int.hpp
index f5333498..6da5ecfa 100644
--- a/src/crwimage_int.hpp
+++ b/src/crwimage_int.hpp
@@ -26,10 +26,10 @@ struct CrwSubDir;
 // type definitions
 
 //! Function pointer for functions to decode Exif tags from a CRW entry
-using CrwDecodeFct = void (*)(const CiffComponent&, const CrwMapping*, Image&, ByteOrder);
+using CrwDecodeFct = std::function<void(const CiffComponent&, const CrwMapping*, Image&, ByteOrder)>;
 
 //! Function pointer for functions to encode CRW entries from Exif tags
-using CrwEncodeFct = void (*)(const Image&, const CrwMapping*, CiffHeader*);
+using CrwEncodeFct = std::function<void(const Image&, const CrwMapping*, CiffHeader*)>;
 
 //! Stack to hold a path of CRW directories
 using CrwDirs = std::stack<CrwSubDir>;
@@ -501,7 +501,7 @@ struct CrwMapping {
   //@{
   //! Default constructor
   CrwMapping(uint16_t crwTagId, uint16_t crwDir, uint32_t size, uint16_t tag, Internal::IfdId ifdId,
-             CrwDecodeFct toExif, CrwEncodeFct fromExif) :
+             const CrwDecodeFct& toExif, const CrwEncodeFct& fromExif) :
       crwTagId_(crwTagId),
       crwDir_(crwDir),
       size_(size),