diff --git a/gr-uhd/lib/gr_uhd_usrp_sink.cc b/gr-uhd/lib/gr_uhd_usrp_sink.cc
index 4598e54..b8b99a4 100644
--- a/gr-uhd/lib/gr_uhd_usrp_sink.cc
+++ b/gr-uhd/lib/gr_uhd_usrp_sink.cc
@@ -45,7 +45,8 @@ public:
             num_channels, num_channels, io_type.size
         )),
         _type(io_type),
-        _nchan(num_channels)
+        _nchan(num_channels),
+        _has_time_spec(_nchan > 1)
     {
         _dev = uhd::usrp::multi_usrp::make(device_addr);
     }
@@ -172,7 +173,7 @@ public:
         //send a mid-burst packet with time spec
         _metadata.start_of_burst = false;
         _metadata.end_of_burst = false;
-        _metadata.has_time_spec = true;
+        _metadata.has_time_spec = _has_time_spec;
 
         size_t num_sent = _dev->get_device()->send(
             input_items, noutput_items, _metadata,
@@ -189,7 +190,7 @@ public:
     bool start(void){
         _metadata.start_of_burst = true;
         _metadata.end_of_burst = false;
-        _metadata.has_time_spec = true;
+        _metadata.has_time_spec = _has_time_spec;
         _metadata.time_spec = get_time_now() + uhd::time_spec_t(0.01);
 
         _dev->get_device()->send(
@@ -217,6 +218,7 @@ protected:
     uhd::usrp::multi_usrp::sptr _dev;
     const uhd::io_type_t _type;
     size_t _nchan;
+    bool _has_time_spec;
     uhd::tx_metadata_t _metadata;
     double _sample_rate;
 };