diff --git a/DCM_SP.v b/DCM_SP.v
index 7e9b5da..e366750 100644
--- a/DCM_SP.v
+++ b/DCM_SP.v
@@ -79,6 +79,8 @@ endgenerate
  
   assign LOCKED = lock_2x && lock_fx;
 
+`else
+ $error ("Unimplemented DCM_SP for non verilator sim.  Should use original Xilinx sim libs not this library." );
 `endif
    
 endmodule