diff --git a/lib/parse_mac.cc b/lib/parse_mac.cc
index 6fdc8a5..5743188 100644
--- a/lib/parse_mac.cc
+++ b/lib/parse_mac.cc
@@ -419,7 +419,7 @@ public:
         str << std::setfill('0') << std::hex << std::setw(2) << (int)addr[0];
 
         for (int i = 1; i < 6; i++) {
-            str << ":" << (int)addr[i];
+            str << ":" << std::setw(2) << (int)addr[i];
         }
 
         return str.str();