diff --git a/passes/techmap/techmap.cc b/passes/techmap/techmap.cc
index 144f596c8..db395315c 100644
--- a/passes/techmap/techmap.cc
+++ b/passes/techmap/techmap.cc
@@ -1041,8 +1041,8 @@ struct TechmapPass : public Pass {
 		log("\n");
 		log("When a port on a module in the map file has the 'techmap_autopurge' attribute\n");
 		log("set, and that port is not connected in the instantiation that is mapped, then\n");
-		log("then a cell port connected only to such wires will be omitted in the mapped\n");
-		log("version of the circuit.\n");
+		log("a cell port connected only to such wires will be omitted in the mapped version\n");
+		log("of the circuit.\n");
 		log("\n");
 		log("All wires in the modules from the map file matching the pattern _TECHMAP_*\n");
 		log("or *._TECHMAP_* are special wires that are used to pass instructions from\n");
diff --git a/techlibs/common/synth.cc b/techlibs/common/synth.cc
index e5013678a..74a484d59 100644
--- a/techlibs/common/synth.cc
+++ b/techlibs/common/synth.cc
@@ -88,6 +88,10 @@ struct SynthPass : public ScriptPass {
 		log("        read/write collision\" (same result as setting the no_rw_check\n");
 		log("        attribute on all memories).\n");
 		log("\n");
+		log("    -extra-map filename\n");
+		log("        source extra rules from the given file to complement the default\n");
+		log("        mapping library in the `techmap` step. this option can be\n");
+		log("        repeated.\n");
 		log("\n");
 		log("The following commands are executed by this synthesis command:\n");
 		help_script();
@@ -96,8 +100,8 @@ struct SynthPass : public ScriptPass {
 
 	string top_module, fsm_opts, memory_opts, abc;
 	bool autotop, flatten, noalumacc, nofsm, noabc, noshare, flowmap, booth;
-
 	int lut;
+	std::vector<std::string> techmap_maps;
 
 	void clear_flags() override
 	{
@@ -115,6 +119,7 @@ struct SynthPass : public ScriptPass {
 		flowmap = false;
 		booth = false;
 		abc = "abc";
+		techmap_maps.clear();
 	}
 
 	void execute(std::vector<std::string> args, RTLIL::Design *design) override
@@ -151,7 +156,7 @@ struct SynthPass : public ScriptPass {
 				flatten = true;
 				continue;
 			}
-			if (args[argidx] == "-lut") {
+			if (args[argidx] == "-lut" && argidx + 1 < args.size()) {
 				lut = atoi(args[++argidx].c_str());
 				continue;
 			}
@@ -192,6 +197,10 @@ struct SynthPass : public ScriptPass {
 				memory_opts += " -no-rw-check";
 				continue;
 			}
+			if (args[argidx] == "-extra-map" && argidx + 1 < args.size()) {
+				techmap_maps.push_back(args[++argidx]);
+				continue;
+			}
 			break;
 		}
 		extra_args(args, argidx, design);
@@ -261,7 +270,17 @@ struct SynthPass : public ScriptPass {
 			run("opt -fast -full");
 			run("memory_map");
 			run("opt -full");
-			run("techmap");
+			if (help_mode) {
+				run("techmap", "                  (unless -extra-map)");	
+				run("techmap -map +/techmap.v -map <inject>", "  (if -extra-map)");
+			} else {
+				std::string techmap_opts;
+				if (!techmap_maps.empty())
+					techmap_opts += " -map +/techmap.v";
+				for (auto fn : techmap_maps)
+					techmap_opts += stringf(" -map %s", fn.c_str());
+				run("techmap" + techmap_opts);
+			}
 			if (help_mode) {
 				run("techmap -map +/gate2lut.v", "(if -noabc and -lut)");
 				run("clean; opt_lut", "           (if -noabc and -lut)");