diff --git a/tcl/Sdc.tcl b/tcl/Sdc.tcl
index 73cdf4fd..75a4688e 100644
--- a/tcl/Sdc.tcl
+++ b/tcl/Sdc.tcl
@@ -1102,9 +1102,6 @@ proc create_clock { args } {
     foreach edge $wave_arg {
       check_float "-waveform edge" $edge
       set edge [time_ui_sta $edge]
-      if { $edge < 0 } {
-	sta_error 340 "negative clock -waveform edge time."
-      }
       if { !$first_edge && $edge < $prev_edge } {
 	sta_error 338 "non-increasing clock -waveform edge times."
       }