diff --git a/gr-uhd/include/gr_uhd_usrp_source.h b/gr-uhd/include/gr_uhd_usrp_source.h
index 36331f7..77c03ac 100644
--- a/gr-uhd/include/gr_uhd_usrp_source.h
+++ b/gr-uhd/include/gr_uhd_usrp_source.h
@@ -259,6 +259,11 @@ public:
     virtual void set_time_unknown_pps(const uhd::time_spec_t &time_spec) = 0;
 
     /*!
+     * \param t start streaming at this time (mboard time).
+     */
+    virtual void set_stream_start_time(double t) = 0; 
+
+    /*!
      * Get access to the underlying uhd dboard iface object.
      * \return the dboard_iface object
      */
diff --git a/gr-uhd/lib/gr_uhd_usrp_source.cc b/gr-uhd/lib/gr_uhd_usrp_source.cc
index 9983489..89fd0be 100644
--- a/gr-uhd/lib/gr_uhd_usrp_source.cc
+++ b/gr-uhd/lib/gr_uhd_usrp_source.cc
@@ -43,7 +44,8 @@ public:
         _type(io_type),
         _nchan(num_channels),
         _stream_now(_nchan == 1),
-        _tmp_buffs(_nchan)
+        _tmp_buffs(_nchan),
+        _stream_start_time(0.0)
     {
         _dev = uhd::usrp::multi_usrp::make(device_addr);
     }
@@ -166,6 +168,10 @@ public:
         return _dev->set_time_unknown_pps(time_spec);
     }
 
+    void set_stream_start_time(double t){
+      _stream_start_time = t;
+    }
+
     uhd::usrp::dboard_iface::sptr get_dboard_iface(size_t chan){
         return _dev->get_rx_dboard_iface(chan);
     }
@@ -209,22 +216,25 @@ public:
         for (size_t i = 0; i < _nchan; i++){
             _tmp_buffs[i] = static_cast<char *>(output_items[i]) + num_samps*_type.size;
         }
-
+        
         //receive all available packets without timeout
         num_samps += _dev->get_device()->recv(
             _tmp_buffs, noutput_items, _metadata,
             _type, uhd::device::RECV_MODE_FULL_BUFF, 0.0
         );
-
+        
         return num_samps;
     }
 
     bool start(void){
         //setup a stream command that starts streaming slightly in the future
-        static const double reasonable_delay = 0.1; //order of magnitude over RTT
+        static const double reasonable_delay = 0.1;
         uhd::stream_cmd_t stream_cmd(uhd::stream_cmd_t::STREAM_MODE_START_CONTINUOUS);
         stream_cmd.stream_now = _stream_now;
-        stream_cmd.time_spec = get_time_now() + uhd::time_spec_t(reasonable_delay);
+        if(_stream_start_time == 0.0)
+          stream_cmd.time_spec = get_time_now() + uhd::time_spec_t(reasonable_delay);
+        else
+          stream_cmd.time_spec = uhd::time_spec_t(_stream_start_time);
         _dev->issue_stream_cmd(stream_cmd);
         return true;
     }
@@ -241,6 +251,7 @@ private:
     bool _stream_now;
     gr_vector_void_star _tmp_buffs;
     uhd::rx_metadata_t _metadata;
+    double _stream_start_time;
 };