diff --git a/passes/techmap/muxcover.cc b/passes/techmap/muxcover.cc
index 4d9c111e7..fa97239f5 100644
--- a/passes/techmap/muxcover.cc
+++ b/passes/techmap/muxcover.cc
@@ -671,14 +671,14 @@ struct MuxcoverPass : public Pass {
 		{
 			const auto &arg = args[argidx];
 			if (arg.size() >= 6 && arg.substr(0,6) == "-mux2=") {
-				cost_mux2 = atoi(arg.substr(6).c_str());
+				cost_mux2 = std::stoi(arg.substr(6));
 				continue;
 			}
 			if (arg.size() >= 5 && arg.substr(0,5) == "-mux4") {
 				use_mux4 = true;
 				if (arg.size() > 5) {
 					if (arg[5] != '=') break;
-					cost_mux4 = atoi(arg.substr(6).c_str());
+					cost_mux4 = std::stoi(arg.substr(6));
 				}
 				continue;
 			}
@@ -686,7 +686,7 @@ struct MuxcoverPass : public Pass {
 				use_mux8 = true;
 				if (arg.size() > 5) {
 					if (arg[5] != '=') break;
-					cost_mux8 = atoi(arg.substr(6).c_str());
+					cost_mux8 = std::stoi(arg.substr(6));
 				}
 				continue;
 			}
@@ -694,12 +694,12 @@ struct MuxcoverPass : public Pass {
 				use_mux16 = true;
 				if (arg.size() > 6) {
 					if (arg[6] != '=') break;
-					cost_mux16 = atoi(arg.substr(7).c_str());
+					cost_mux16 = std::stoi(arg.substr(7));
 				}
 				continue;
 			}
 			if (arg.size() >= 6 && arg.substr(0,6) == "-dmux=") {
-				cost_dmux = atoi(arg.substr(6).c_str());
+				cost_dmux = std::stoi(arg.substr(6));
 				continue;
 			}
 			if (arg == "-nodecode") {