diff --git a/src/ISO8601.cpp b/src/ISO8601.cpp
index ba2d68d7e..85813a4d3 100644
--- a/src/ISO8601.cpp
+++ b/src/ISO8601.cpp
@@ -1229,6 +1229,20 @@ void ISO8601d::operator-- (int)
   _date = yesterday._date;
 }
 
+////////////////////////////////////////////////////////////////////////////////
+// Prefix increment by one day.
+void ISO8601d::operator++ ()
+{
+  ISO8601d tomorrow = (startOfDay () + 90001).startOfDay ();
+  tomorrow = ISO8601d (tomorrow.month (),
+                       tomorrow.day (),
+                       tomorrow.year (),
+                       hour (),
+                       minute (),
+                       second ());
+  _date = tomorrow._date;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 void ISO8601p::clear ()
 {
diff --git a/src/ISO8601.h b/src/ISO8601.h
index c3a24ab61..0694a149c 100644
--- a/src/ISO8601.h
+++ b/src/ISO8601.h
@@ -87,6 +87,7 @@ public:
   time_t operator- (const ISO8601d&);
   void operator-- ();    // Prefix
   void operator-- (int); // Postfix
+  void operator++ ();    // Prefix
 
 private:
   void clear ();