diff --git a/example/simplesvr.cc b/example/simplesvr.cc
index a84bb1e..17a9e98 100644
--- a/example/simplesvr.cc
+++ b/example/simplesvr.cc
@@ -46,7 +46,7 @@ string dump_multipart_files(const MultipartFormDataMap &files) {
     snprintf(buf, sizeof(buf), "content type: %s\n", file.content_type.c_str());
     s += buf;
 
-    snprintf(buf, sizeof(buf), "text length: %lu\n", file.content.size());
+    snprintf(buf, sizeof(buf), "text length: %zu\n", file.content.size());
     s += buf;
 
     s += "----------------\n";