diff --git a/logger.cpp b/logger.cpp
index dcb0816..1f3dfdf 100644
--- a/logger.cpp
+++ b/logger.cpp
@@ -39,7 +39,7 @@ void logger::write_prefix(loglevel level, const char* file, int line, const char
     char dtstamp[20];
     std::strftime(dtstamp, 20, "%F %T", std::localtime(&secs.tv_sec));
 
-    std::cerr << dtstamp << "." << std::setw(3) << ms << " ";
+    std::cerr << dtstamp << "." << std::setfill('0') << std::setw(3) << ms << " ";
     std::cerr << _name << "[" << ::getpid() << "] ";
     std::cerr << file << ":" << line << " " << func << "() ";
     std::cerr << '[' << loglevel_desc(level) << "] ";