diff --git a/luna/Format.cpp b/luna/Format.cpp
index 6f3a2e56..7d086876 100644
--- a/luna/Format.cpp
+++ b/luna/Format.cpp
@@ -170,7 +170,7 @@ static void parse_length(const char** format, flags_t& flags)
         (*format)++;
         break;
     case 'z':
-        flags |= (sizeof(size_t) == sizeof(long)) ? FLAG_LONG : FLAG_LONG_LONG;
+        flags |= (sizeof(usize) == sizeof(long)) ? FLAG_LONG : FLAG_LONG_LONG;
         (*format)++;
         break;
     default: break;