diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc
index 2838449b..56c631f3 100644
--- a/kernel/rtlil.cc
+++ b/kernel/rtlil.cc
@@ -490,9 +490,9 @@ namespace {
 			}
 
 			for (auto &conn : cell->connections()) {
-				if (conn.first.size() != 2 || conn.first.at(0) != '\\')
+				if (conn.first.size() != 2 || conn.first[0] != '\\')
 					error(__LINE__);
-				if (strchr(ports, conn.first.at(1)) == NULL)
+				if (strchr(ports, conn.first[1]) == NULL)
 					error(__LINE__);
 			}
 		}
diff --git a/kernel/rtlil.h b/kernel/rtlil.h
index 502969a1..ab15024e 100644
--- a/kernel/rtlil.h
+++ b/kernel/rtlil.h
@@ -185,12 +185,11 @@ namespace RTLIL
 		bool operator==(const char *rhs) const { return str() == rhs; }
 		bool operator!=(const char *rhs) const { return str() != rhs; }
 
-		char at(size_t i) const {
-			return c_str()[i];
-		}
-
 		char operator[](size_t i) const {
-			return c_str()[i];
+			const char *p = c_str();
+			for (; i != 0; i--, p++) 
+				log_assert(*p != 0);
+			return *p;
 		}
 
 		std::string substr(size_t pos = 0, size_t len = std::string::npos) const {
diff --git a/passes/sat/expose.cc b/passes/sat/expose.cc
index affd685e..e856fdf7 100644
--- a/passes/sat/expose.cc
+++ b/passes/sat/expose.cc
@@ -50,7 +50,7 @@ static bool consider_cell(RTLIL::Design *design, std::set<RTLIL::IdString> &dff_
 {
 	if (cell->name[0] == '$' || dff_cells.count(cell->name))
 		return false;
-	if (cell->type.at(0) == '\\' && !design->modules_.count(cell->type))
+	if (cell->type[0] == '\\' && !design->modules_.count(cell->type))
 		return false;
 	return true;
 }