diff --git a/kernel/log.cc b/kernel/log.cc
index 131291a3c..7ddf9cfe1 100644
--- a/kernel/log.cc
+++ b/kernel/log.cc
@@ -216,7 +216,7 @@ void log_formatted_string(std::string_view format, std::string str)
 	logv_string(format, std::move(str));
 }
 
-static void logv_header(RTLIL::Design *design, const char *format, va_list ap)
+void log_formatted_header(RTLIL::Design *design, std::string_view format, std::string str)
 {
 	bool pop_errfile = false;
 
@@ -235,7 +235,7 @@ static void logv_header(RTLIL::Design *design, const char *format, va_list ap)
 		header_id += stringf("%s%d", header_id.empty() ? "" : ".", c);
 
 	log("%s. ", header_id.c_str());
-	logv(format, ap);
+	log_formatted_string(format, std::move(str));
 	log_flush();
 
 	if (log_hdump_all)
@@ -414,14 +414,6 @@ void log_file_error(const string &filename, int lineno,
 	logv_file_error(filename, lineno, format, ap);
 }
 
-void log_header(RTLIL::Design *design, const char *format, ...)
-{
-	va_list ap;
-	va_start(ap, format);
-	logv_header(design, format, ap);
-	va_end(ap);
-}
-
 void log_warning(const char *format, ...)
 {
 	va_list ap;
diff --git a/kernel/log.h b/kernel/log.h
index d1a438e77..9cdc00181 100644
--- a/kernel/log.h
+++ b/kernel/log.h
@@ -122,7 +122,6 @@ extern int log_debug_suppressed;
 [[noreturn]] void logv_file_error(const string &filename, int lineno, const char *format, va_list ap);
 
 
-void log_header(RTLIL::Design *design, const char *format, ...) YS_ATTRIBUTE(format(printf, 2, 3));
 void log_warning(const char *format, ...) YS_ATTRIBUTE(format(printf, 1, 2));
 void log_experimental(const char *format, ...) YS_ATTRIBUTE(format(printf, 1, 2));
 
@@ -154,6 +153,13 @@ inline void log(FmtString<TypeIdentity<Args>...> fmt, Args... args)
 	log_formatted_string(fmt.format_string(), fmt.format(args...));
 }
 
+void log_formatted_header(RTLIL::Design *design, std::string_view format, std::string str);
+template <typename... Args>
+inline void log_header(RTLIL::Design *design, FmtString<TypeIdentity<Args>...> fmt, Args... args)
+{
+	log_formatted_header(design, fmt.format_string(), fmt.format(args...));
+}
+
 static inline void log_suppressed() {
 	if (log_debug_suppressed && !log_make_debug) {
 		log("<suppressed ~%d debug messages>\n", log_debug_suppressed);
diff --git a/passes/opt/opt.cc b/passes/opt/opt.cc
index 146c21cce..ec5760cd9 100644
--- a/passes/opt/opt.cc
+++ b/passes/opt/opt.cc
@@ -196,7 +196,7 @@ struct OptPass : public Pass {
 		design->sort();
 		design->check();
 
-		log_header(design, fast_mode ? "Finished fast OPT passes.\n" : "Finished OPT passes. (There is nothing left to do.)\n");
+		log_header(design, "Finished fast OPT passes.%s\n", fast_mode ? "" : " (There is nothing left to do.)");
 		log_pop();
 	}
 } OptPass;