diff --git a/src/fstring.cpp b/src/fstring.cpp
index cb3d800a..49cddf9c 100644
--- a/src/fstring.cpp
+++ b/src/fstring.cpp
@@ -292,6 +292,16 @@ FString& FString::operator << (const uInt64 num)
   return *this;
 }
 
+//----------------------------------------------------------------------
+#if defined(__APPLE__) && defined(__MACH__)
+FString& FString::operator << (const std::size_t num)
+{
+  FString numstr(FString().setNumber(num));
+  _insert (length, numstr.length, numstr.string);
+  return *this;
+}
+#endif
+
 //----------------------------------------------------------------------
 FString& FString::operator << (const float num)
 {
diff --git a/src/include/final/fstring.h b/src/include/final/fstring.h
index 35799f6b..4f1c16b6 100644
--- a/src/include/final/fstring.h
+++ b/src/include/final/fstring.h
@@ -120,6 +120,9 @@ class FString
     FString& operator << (const uInt32);
     FString& operator << (const sInt64);
     FString& operator << (const uInt64);
+#if defined(__APPLE__) && defined(__MACH__)
+    FString& operator << (const std::size_t);
+#endif
     FString& operator << (const float);
     FString& operator << (const double);
     FString& operator << (const lDouble);