diff --git a/passes/techmap/abc9_exe.cc b/passes/techmap/abc9_exe.cc
index ccfc7a7f8..651a8375c 100644
--- a/passes/techmap/abc9_exe.cc
+++ b/passes/techmap/abc9_exe.cc
@@ -368,6 +368,26 @@ struct Abc9ExePass : public Pass {
 		log("        of output quality):\n");
 		log("%s\n", fold_abc9_cmd(RTLIL::constpad.at("abc9.script.default.fast").substr(1,std::string::npos)).c_str());
 		log("\n");
+		log("    -constr <file>\n");
+		log("        pass this file with timing constraints to ABC.\n");
+		log("        use with -liberty.\n");
+		log("\n");
+		log("        a constr file contains two lines:\n");
+		log("            set_driving_cell <cell_name>\n");
+		log("            set_load <floating_point_number>\n");
+		log("\n");
+		log("        the set_driving_cell statement defines which cell type is assumed to\n");
+		log("        drive the primary inputs and the set_load statement sets the load in\n");
+		log("        femtofarads for each primary output.\n");
+		log("\n");
+		log("    -liberty <file>\n");
+		log("        read the given Liberty file as a description of the target cell library.\n");
+		log("        this option can be used multiple times.\n");
+		log("\n");
+		log("    -dont_use <cell_name>\n");
+		log("        avoid usage of the technology cell <cell_name> when mapping the design.\n");
+		log("        this option can be used multiple times.\n");
+		log("\n");
 		log("    -D <picoseconds>\n");
 		log("        set delay target. the string {D} in the default scripts above is\n");
 		log("        replaced by this option when used, and an empty string otherwise\n");