diff --git a/frontends/ast/genrtlil.cc b/frontends/ast/genrtlil.cc
index 84f2f9d73..7518e4a3e 100644
--- a/frontends/ast/genrtlil.cc
+++ b/frontends/ast/genrtlil.cc
@@ -2195,7 +2195,7 @@ RTLIL::SigSpec AstNode::genRTLIL(int width_hint, bool sign_hint)
 			int sz = children.size();
 			if (str == "$info") {
 				if (sz > 0)
-					log_file_info(*location.begin.filename, location.begin.line, "%s.\n", children[0]->str.c_str());
+					log_file_info(*location.begin.filename, location.begin.line, "%s.\n", children[0]->str);
 				else
 					log_file_info(*location.begin.filename, location.begin.line, "\n");
 			} else if (str == "$warning") {
diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index d4e78b730..d249bc8ad 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -161,7 +161,7 @@ Fmt AstNode::processFormat(int stage, bool sformat_like, int default_base, size_
 			arg.sig = node_arg->bitsAsConst();
 			arg.signed_ = node_arg->is_signed;
 		} else if (may_fail) {
-			log_file_info(*location.begin.filename, location.begin.line, "Skipping system task `%s' with non-constant argument at position %zu.\n", str.c_str(), index + 1);
+			log_file_info(*location.begin.filename, location.begin.line, "Skipping system task `%s' with non-constant argument at position %zu.\n", str, index + 1);
 			return Fmt();
 		} else {
 			log_file_error(*location.begin.filename, location.begin.line, "Failed to evaluate system task `%s' with non-constant argument at position %zu.\n", str, index + 1);