diff --git a/src/Duration.cpp b/src/Duration.cpp
index d82b98bc1..db0cd07c5 100644
--- a/src/Duration.cpp
+++ b/src/Duration.cpp
@@ -308,7 +308,7 @@ std::string Duration::formatPrecise () const
 std::string Duration::formatSeconds () const
 {
   char formatted[24];
-  sprintf (formatted, "%s%ldsec", (_negative ? "-" : ""), _secs);
+  sprintf (formatted, "%s%llusec", (_negative ? "-" : ""), (unsigned long long)_secs);
   return std::string (formatted);
 }