diff --git a/src/ISO8601.cpp b/src/ISO8601.cpp
index 3e740296f..444907c3b 100644
--- a/src/ISO8601.cpp
+++ b/src/ISO8601.cpp
@@ -854,6 +854,12 @@ ISO8601d ISO8601d::startOfWeek () const
   return ISO8601d (sow.month (), sow.day (), sow.year ());
 }
 
+////////////////////////////////////////////////////////////////////////////////
+ISO8601d ISO8601d::startOfMonth () const
+{
+  return ISO8601d (month (), 1, year ());
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Static
 bool ISO8601d::leapYear (int year)
diff --git a/src/ISO8601.h b/src/ISO8601.h
index 97f9d6f39..062a0c961 100644
--- a/src/ISO8601.h
+++ b/src/ISO8601.h
@@ -48,6 +48,7 @@ public:
 
   ISO8601d startOfDay () const;
   ISO8601d startOfWeek () const;
+  ISO8601d startOfMonth () const;
 
   static bool leapYear (int);
   static int daysInMonth (int, int);