diff --git a/sflphone-common/src/audio/audiortp/ZrtpSessionCallback.h b/sflphone-common/src/audio/audiortp/ZrtpSessionCallback.h
index 2fad01eed47517cfda17904a1563a9a1430b08f2..c9d2acadff0bf7c9caba62ecefe3ee24309fc81e 100644
--- a/sflphone-common/src/audio/audiortp/ZrtpSessionCallback.h
+++ b/sflphone-common/src/audio/audiortp/ZrtpSessionCallback.h
@@ -30,6 +30,9 @@
 
 #ifndef __SFL_ZRTP_CALLBACK_H__
 #define __SFL_ZRTP_CALLBACK_H__
+#include <cstddef>
+
+using std::ptrdiff_t;
 
 #include <libzrtpcpp/zrtpccrtp.h>
 #include <libzrtpcpp/ZrtpQueue.h>