diff --git a/frontends/ast/ast.cc b/frontends/ast/ast.cc
index 313161fc3..9af355109 100644
--- a/frontends/ast/ast.cc
+++ b/frontends/ast/ast.cc
@@ -1922,11 +1922,9 @@ void AstModule::loadconfig() const
 	flag_autowire = autowire;
 }
 
-void AstNode::input_error(const char *format, ...) const
+void AstNode::formatted_input_error(std::string str) const
 {
-	va_list ap;
-	va_start(ap, format);
-	logv_file_error(*location.begin.filename, location.begin.line, format, ap);
+	log_formatted_file_error(*location.begin.filename, location.begin.line, std::move(str));
 }
 
 YOSYS_NAMESPACE_END
diff --git a/frontends/ast/ast.h b/frontends/ast/ast.h
index fdf4d1ec9..fd8ecddd7 100644
--- a/frontends/ast/ast.h
+++ b/frontends/ast/ast.h
@@ -378,7 +378,12 @@ namespace AST
 		AstNode *get_struct_member() const;
 
 		// helper to print errors from simplify/genrtlil code
-		[[noreturn]] void input_error(const char *format, ...) const YS_ATTRIBUTE(format(printf, 2, 3));
+		[[noreturn]] void formatted_input_error(std::string str) const;
+		template <typename... Args>
+		[[noreturn]] void input_error(FmtString<TypeIdentity<Args>...> fmt, const Args &... args) const
+		{
+			formatted_input_error(fmt.format(args...));
+		}
 	};
 
 	// process an AST tree (ast must point to an AST_DESIGN node) and generate RTLIL code