diff --git a/src/seeder/util.h b/src/seeder/util.h
--- a/src/seeder/util.h
+++ b/src/seeder/util.h
@@ -44,9 +44,9 @@
     nanosleep(&wa, nullptr);
 }
 
-std::string vstrprintf(const std::string &format, va_list ap);
+std::string vstrprintf(const char *format, va_list ap);
 
-static inline std::string strprintf(const std::string &format, ...) {
+static inline std::string strprintf(const char *format, ...) {
     va_list arg_ptr;
     va_start(arg_ptr, format);
     std::string ret = vstrprintf(format, arg_ptr);
diff --git a/src/seeder/util.cpp b/src/seeder/util.cpp
--- a/src/seeder/util.cpp
+++ b/src/seeder/util.cpp
@@ -2,7 +2,7 @@
 
 #include <cstdio>
 
-std::string vstrprintf(const std::string &format, va_list ap) {
+std::string vstrprintf(const char *format, va_list ap) {
     char buffer[50000];
     char *p = buffer;
     int limit = sizeof(buffer);
@@ -10,7 +10,7 @@
     loop {
         va_list arg_ptr;
         va_copy(arg_ptr, ap);
-        ret = vsnprintf(p, limit, format.c_str(), arg_ptr);
+        ret = vsnprintf(p, limit, format, arg_ptr);
         va_end(arg_ptr);
         if (ret >= 0 && ret < limit) break;
         if (p != buffer) delete[] p;