diff --git a/src/ISO8601.cpp b/src/ISO8601.cpp
index 797828ab8..3e740296f 100644
--- a/src/ISO8601.cpp
+++ b/src/ISO8601.cpp
@@ -846,6 +846,14 @@ ISO8601d ISO8601d::startOfDay () const
   return ISO8601d (month (), day (), year ());
 }
 
+////////////////////////////////////////////////////////////////////////////////
+ISO8601d ISO8601d::startOfWeek () const
+{
+  ISO8601d sow (_date);
+  sow -= (dayOfWeek () * 86400);
+  return ISO8601d (sow.month (), sow.day (), sow.year ());
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Static
 bool ISO8601d::leapYear (int year)
diff --git a/src/ISO8601.h b/src/ISO8601.h
index f5fbc1e9c..97f9d6f39 100644
--- a/src/ISO8601.h
+++ b/src/ISO8601.h
@@ -47,6 +47,7 @@ public:
   bool parse (const std::string&, std::string::size_type&, const std::string& format = "");
 
   ISO8601d startOfDay () const;
+  ISO8601d startOfWeek () const;
 
   static bool leapYear (int);
   static int daysInMonth (int, int);