diff --git a/passes/cmds/icell_liberty.cc b/passes/cmds/icell_liberty.cc
index 19692fa01..9b89c1125 100644
--- a/passes/cmds/icell_liberty.cc
+++ b/passes/cmds/icell_liberty.cc
@@ -18,19 +18,27 @@
  */
 #include "kernel/yosys.h"
 #include "kernel/celltypes.h"
+#include "kernel/ff.h"
 
 USING_YOSYS_NAMESPACE
 PRIVATE_NAMESPACE_BEGIN
 
 struct LibertyStubber {
 	CellTypes ct;
-	CellTypes ct_ff;
 	LibertyStubber() {
 		ct.setup();
 		ct.setup_internals_ff();
 	}
 	void liberty_prefix(std::ostream& f)
 	{
+		f << "/*\n";
+		f << stringf("Models interfaces of select Yosys internal cell.\n");
+		f << stringf("Likely contains INCORRECT POLARITIES.\n");
+		f << stringf("Impractical for any simulation, synthesis, or timing.\n");
+		f << stringf("Intended purely for SDC expansion.\n");
+		f << stringf("Do not microwave or tumble dry.\n");
+		f << stringf("Generated by %s\n", yosys_maybe_version());
+		f << "*/\n";
 		f << "library (yosys) {\n";
 		f << "\tinput_threshold_pct_fall : 50;\n";
 		f << "\tinput_threshold_pct_rise : 50;\n";
@@ -45,6 +53,76 @@ struct LibertyStubber {
 	{
 		f << "}\n";
 	}
+	struct LibertyItemizer {
+		std::ostream& f;
+		int indent;
+		LibertyItemizer(std::ostream& f) : f(f), indent(0) {};
+		void item(std::string key, std::string val)
+		{
+			f << std::string(indent, '\t') << key << " : \"" << val << "\";\n";
+		}
+	};
+	void liberty_flop(Module* base, Module* derived, std::ostream& f)
+	{
+		auto base_name = base->name.str().substr(1);
+		auto derived_name = derived->name.str().substr(1);
+
+		FfTypeData ffType(base_name);
+		LibertyItemizer i(f);
+
+		if (ffType.has_gclk) {
+			log_warning("Formal flip flop %s can't be modeled\n", base_name.c_str());
+			return;
+		}
+		if (ffType.has_ce) {
+			log_warning("DFFE %s can't be modeled\n", base_name.c_str());
+			return;
+		}
+
+		f << "\tcell (\"" << derived_name << "\") {\n";
+		auto& base_type = ct.cell_types[base_name];
+		i.indent = 3;
+		for (auto x : derived->ports) {
+			bool is_input = base_type.inputs.count(x);
+			bool is_output = base_type.outputs.count(x);
+			f << "\t\tpin (" << RTLIL::unescape_id(x.str()) << ") {\n";
+			if (is_input && !is_output) {
+				i.item("direction", "input");
+			} else if (!is_input && is_output) {
+				i.item("direction", "output");
+			} else {
+				i.item("direction", "inout");
+			}
+			if (RTLIL::unescape_id(x) == "CLK" || RTLIL::unescape_id(x) == "C")
+				i.item("clock", "true");
+			if (RTLIL::unescape_id(x) == "Q")
+				i.item("function", "IQ");
+			f << "\t\t}\n";
+		}
+
+		f << "\t\tff (\"IQ\",\"IQ_N\") {\n";
+		i.indent = 3;
+		// TODO polarities?
+		if (ffType.has_clk) {
+			auto pin = ffType.is_fine ? "C" : "CLK";
+			i.item("clocked_on", pin);
+		}
+		if (ffType.has_arst) {
+			auto meaning = (ffType.val_arst == State::S1) ? "preset" : "clear";
+			auto pin = ffType.is_fine ? "R" : "ARST";
+			i.item(meaning, pin);
+		}
+		auto next_state = ffType.has_ce ? "D & EN" : "D";
+		i.item("next_state", next_state);
+		f << "\t\t}\n";
+
+
+		// bool has_aload;
+		// bool has_srst;
+		// bool has_arst;
+		// bool has_sr;
+		f << "\t}\n";
+	}
 	void liberty_cell(Module* base, Module* derived, std::ostream& f)
 	{
 		auto base_name = base->name.str().substr(1);
@@ -53,6 +131,10 @@ struct LibertyStubber {
 			log_debug("skip skeleton for %s\n", base_name.c_str());
 			return;
 		}
+
+		if (RTLIL::builtin_ff_cell_types().count(base_name))
+			return liberty_flop(base, derived, f);
+
 		auto& base_type = ct.cell_types[base_name];
 		f << "\tcell (\"" << derived_name << "\") {\n";
 		for (auto x : derived->ports) {
@@ -73,7 +155,7 @@ struct LibertyStubber {
 };
 
 struct IcellLiberty : Pass {
-	IcellLiberty() : Pass("icell_liberty", "derive box modules") {}
+	IcellLiberty() : Pass("icell_liberty", "write Liberty interfaces for used internal cells") {}
 	void help() override
 	{
 		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|