1 files changed, 4 insertions, 0 deletions
diff --git a/techlibs/xilinx/synth_xilinx.cc b/techlibs/xilinx/synth_xilinx.cc
index 2c5686a35..6dd769055 100644
--- a/techlibs/xilinx/synth_xilinx.cc
+++ b/techlibs/xilinx/synth_xilinx.cc
@@ -306,6 +306,10 @@ struct SynthXilinxPass : public ScriptPass
 			run("proc");
 			if (flatten || help_mode)
 				run("flatten", "(with '-flatten')");
+			active_design->scratchpad_unset("tribuf.added_something");
+			run("tribuf -logic");
+			if (!do_iopad && active_design->scratchpad_get_bool("tribuf.added_something"))
+				log_error("Tristate buffers are unsupported without the '-iopad' option.\n");
 			run("tribuf -logic");
 			run("deminout");
 			run("opt_expr");