diff --git a/src/runtime_linux.cc b/src/runtime_linux.cc
index 89fb627..b614a63 100644
--- a/src/runtime_linux.cc
+++ b/src/runtime_linux.cc
@@ -65,7 +65,7 @@
       index = text.find(')');
       text.erase(index, 1);
     }
-    std::string log_line(StringPrintf("\t#%02d ", i) + function_name + text);
+    std::string log_line(StringPrintf("\t#%02zd ", i) + function_name + text);
     LogMessage(filename.c_str(), -1, ERROR, -1).stream() << log_line;
   }