diff --git a/include/fc/time.hpp b/include/fc/time.hpp
index 6a6146d..204d586 100644
--- a/include/fc/time.hpp
+++ b/include/fc/time.hpp
@@ -9,7 +9,7 @@
 #endif //// _MSC_VER
 
 namespace fc {
-  class microseconds { 
+  class microseconds {
     public:
         explicit microseconds( int64_t c = 0) :_count(c){}
         static microseconds maximum() { return microseconds(0x7fffffffffffffffll); }
@@ -23,10 +23,11 @@ namespace fc {
         friend bool operator<(const microseconds& a, const microseconds& b){ return a._count < b._count; }
         friend bool operator<=(const microseconds& a, const microseconds& b){ return a._count <= b._count; }
         microseconds& operator+=(const microseconds& c) { _count += c._count; return *this; }
+        microseconds& operator-=(const microseconds& c) { _count -= c._count; return *this; }
         int64_t count()const { return _count; }
     private:
         friend class time_point;
-        int64_t      _count; 
+        int64_t      _count;
   };
   inline microseconds seconds( int64_t s ) { return microseconds( s * 1000000 ); }
   inline microseconds milliseconds( int64_t s ) { return microseconds( s * 1000 ); }
@@ -34,14 +35,14 @@ namespace fc {
   inline microseconds hours(int64_t h) { return minutes(60*h); }
   inline microseconds days(int64_t d) { return hours(24*d); }
 
-  class time_point { 
+  class time_point {
     public:
         explicit time_point( microseconds e = microseconds() ) :elapsed(e){}
         static time_point now();
         static time_point maximum() { return time_point( microseconds::maximum() ); }
         static time_point min() { return time_point();                      }
         operator fc::string()const;
-  
+
         static time_point from_iso_string( const fc::string& s );
 
         const microseconds& time_since_epoch()const { return elapsed; }
@@ -53,17 +54,18 @@ namespace fc {
         bool   operator ==( const time_point& t )const                              { return elapsed._count ==t.elapsed._count; }
         bool   operator !=( const time_point& t )const                              { return elapsed._count !=t.elapsed._count; }
         time_point&  operator += ( const microseconds& m)                           { elapsed+=m; return *this;                 }
+        time_point&  operator -= ( const microseconds& m)                           { elapsed-=m; return *this;                 }
         time_point   operator + (const microseconds& m) const { return time_point(elapsed+m); }
         time_point   operator - (const microseconds& m) const { return time_point(elapsed-m); }
         microseconds operator - (const time_point& m) const { return microseconds(elapsed.count() - m.elapsed.count()); }
     private:
-        microseconds elapsed; 
+        microseconds elapsed;
   };
 
   /**
    *  A lower resolution time_point accurate only to seconds from 1970
    */
-  class time_point_sec 
+  class time_point_sec
   {
     public:
         time_point_sec()
@@ -90,6 +92,7 @@ namespace fc {
         friend bool      operator == ( const time_point_sec& a, const time_point_sec& b ) { return a.utc_seconds == b.utc_seconds; }
         friend bool      operator != ( const time_point_sec& a, const time_point_sec& b ) { return a.utc_seconds != b.utc_seconds; }
         time_point_sec&  operator += ( uint32_t m ) { utc_seconds+=m; return *this; }
+        time_point_sec&  operator -= ( uint32_t m ) { utc_seconds-=m; return *this; }
 
         friend time_point   operator - ( const time_point_sec& t, const microseconds& m )   { return time_point(t) - m;             }
         friend microseconds operator - ( const time_point_sec& t, const time_point_sec& m ) { return time_point(t) - time_point(m); }